Do you ever get the response?

A few things to note here...

One, if you ask a girl "Do you have a boyfriend?" or say "So... are you seeing anyone?" or something like that, it implies on a subconscious level that you are interested in knowing this information because you want to know if you have a chance of being her boyfriend. Even if you have no such desire. Oftentimes girls will reply "Umm... kind of" for a few reasons. One may be that she's single but just wants to get rid of you because you've asked her the same question as three or four other guys already that day. Maybe she's single but really interested in some other guy. It could be that she does have a boyfriend, and things aren't going so hot so she's being very honest (hardly ever happens.) Another may be that she has a boyfriend but she's more interested in you (happens more than the last one, actually.) And finally, she may have a boyfriend who she's madly in love with and doesn't want anything to do with you (this and the first one are the most common.)

In any case, asking questions like this is a bad idea. The best way to find out if someone is single is to be totally direct and not imply anything with your question. Look her straight in the eye and ask her, "Are you single?" This communicates ONLY that you want to know if she's single. She's left wondering why you want to know - is it because you want to take her on a date? Wanna do her? Wanna have a relationship? Wanna make fun of her for having a dumb boyfriend? Wanna make fun of her for being single? And her only choice is to just respond "yes" or "no." Sometimes you'll get the occasional "sort of" and you can say something like "Yeah, I understand what you mean by 'sort of'... my girlfriend would get pretty mad if she found out about my mistress... and I don't even wanna know what my WIFE would say!" And that will get her laughing, break the ice between you, and she'll finally answer your question directly. And if she asks you why you want to know, you can either tell her the simple truth - that you think she's attractive - or, even better, you can say something like "Well, I'm doing a survey to see how many ugly girls and how many attractive girls are single, kinda figure out the ratio there." And if she asks if she's an ugly girl or an attractive one, just kinda laugh and shake your head at her like she's ridiculous for being so insecure, and DON'T answer. Just say "...Are you gonna answer the question or not?" If she gives you resistance and won't answer, just shrug and go "Okay, I'll come back to you later when you're not so difficult." Then to offset the sting of those words, give her a wink and a smile.

Mixed signals, man. Girls do this to guys ALL THE TIME (hence the "umm... i sort of have a boyfriend" lines) ... do it to them first, and they'll want to be around you, just as much as guys want to be around girls who give THEM mixed signals... for some weird reason.

Jam it back in, in the dark.

No no, be honest, and straight-out, but ... it's like economics. The minute something is in demand, the price goes up. Same with girls - once they know they're wanted, the price goes up... no wait, that's hookers. Once they know they're wanted, they make themselves more difficult to GET.

There's a difference between lying, and joking around with or busting on somebody. Think of how you would act with your very best friend... you'll say things that are edgy, sometimes ALMOST insulting that would make you both laugh, things like that. I myself would say "Okay, I'll come back later when you're not being such a difficult bastard" to my best friend, and grin at him to let him know I was joking. Of course, I wouldn't call a woman I just met a "bitch" (or really ANY woman, unless she was one) but all the rest of it will work great.

It's not really lying and it's not really mixed signals, but it IS a way to get them thinking about you as totally different from any other guy.

There's nowhere I can't reach.

Read the above.
Repeat it.

Then if you still feel you HAVE to know for some weird reason, use my technique. I used it last night, but slightly differently.
Me: "I'm taking you out."
Her: "Uh... wh... what?"
Me: "What? Are you single?"
Her: "Well, yeah..."
Me: "Okay, then I'm taking you out."
Her: "Wow. Okay. I'm... still in shock mode, no guy has ever been that direct before..."
Me: "Yeah, interesting, isn't it? Way better than 'Uhh... do you have a boyfriend?' or 'So... would you like to go out sometime, like, i dunno, to a movie or something?'"
Her: "Definitely. HEY! Let's go to the ghost town after!"

And so on.

Most amazing jew boots

Eh. I'm not one to say that one thing will always work without exception - just that it HAS so far for me... and honestly I can say I've gotten about ten times as many dates THIS way, than I ever did a year or so ago being the overly-nice gentleman about asking girls out. When you make a big deal about it, the girl makes a big deal out of it, and gets uncomfortable.
Me: "I was wondering if you'd like to go out to dinner sometime."
Her thoughts: "...well that was unoriginal. But he is a nice guy. I guess I could..." She says: "Sure, that'd be fun."
Me: "Great!"
Her, an indefinite amount of time later: "Hey, sorry, um, I can't go, I had something come up, maybe some other time, okay?"
Me: "Okay, cool, yeah no big deal." *... YU H8? *

Sound familiar, at least vaguely?

I am a dolphin, do you want me on your body?

The reason they back out is simple... they think it over and decide that it's not worth the effort, or they get scared of you taking it all too seriously, or something along those lines. Harsh, but true.

The best "date" is, in my opinion, one where you can have fun and converse. Movies and food are quite possibly the worst two date ideas ever, which is funny cause they're the traditional fallback dates.
Go out for some coffee, like you mentioned, but make it less about the coffee and more about talking with each other and enjoying each other's company. Don't make it too long, leave when things seem great, like they couldn't get any better - it'll make her want to see you again even MORE.
If you prefer doing something more active, the best date I ever went on, we went and played tennis (we both sucked) and then ran through the sprinklers (yeah, first grade anyone?) and then went back to her place and had brownies or something, then when I sensed things were about to wind down, I left. It was awesome. Total fun, and you could practically see the attraction building.

But I don't think you should be taking my word for any of this, despite how accurate it is. After all... my GFF rating shows just how many asshats think I'm a loser.

I find that hilarious

I was speaking idiomatically.