Let me interject some thoughts into this subject.
First off, if you are walking around thinking you're a "nice guy", and the women you like, shower attention on them, put them on pedestals and are only doing things for them in the attempt to win their favor (i.e., listening to her problems, buying her stuff just because, you want them to like you romantically) you aren't nice guys. Nice guys don't have ulterior motives. "I do so much for my friend X, and she likes a'holes, why doesn't she like me."
Secondly, if you are going to be a wuss and never ask a girl out because you think sitting on your hands and waiting for opportunity to fall into your lap, then you may be a nice guy but you're also an idiot.
Also, as other people have said, don't put women on a pedestal and let them walk all over you.
In the end, I kinda do chuckle that people use the "I'm a nice guy." as some sort of victim card. Some people need an excuse of why they are unsuccessful with women but fail to realize that when some girls say "You're a nice guy but..." pretty much means, "I'm not attracted to you."
Seriously, all you nice guys out there, drop a pair, and just ask her out already or stop sitting on your hands waiting for opportunity and stop keeping that friend around because you believe one day her feelings may change.