It's cool because we get to sleep with hot, sexy men AND hot, sexy women. The same reason why it's cool to be a switch -- and I should know, being both.
Seriously -- yeah, there are a lot of young women who want to be bi because it seems rebellious or gets guys' attention. Personally, I don't know if I "flaunt" my sexuality any more than most hetero people I know do -- I love both my husband and my girlfriend (we're poly; I'm not cheating), and I don't have any desire to hide my feelings for either of them. I do want people to know that I'm bi, mostly because how will I find partners if people don't know what I like?
As for being "slutty," frankly I'm proud of all the men *and* women I've been with. The people I've played with have all been special and interesting in their own ways, and I wouldn't do something if I wasn't going to own it and be proud of it. I don't see anything to be ashamed of.
One thing I don't understand, though: why do people think it's sexier for a submissive woman with a dominant male partner to be bi, when obviously it would be subbie-er and kinkier for her to not be bi, but be willing to do it anyway for the excitement of her Dom?
In general it is definitely harder for bi guys. I think a big part of it is that during the height of AIDS hysteria, a lot of media sources made it seem like the easiest way for a woman to get HIV was to sleep with a man who was also sleeping with me. Also, the gay male subculture can be kind of exclusive at times and isn't really accepting of bi men, which my bi male friends tell me makes it hard to find partners.
Personally, though, I love bi guys. I think they're pretty much the hottest, probably for the same reasons that a lot of straight men think bi women are.