-Did you like online dating? Did you meet your significant other that way?
I think for the most part, online dating is great. I met my gf online four years ago (although I didn't set out to meet anyone, really, it was through a blog site). We were friends for a year and have been together for 3. When I was single I went on a few dates from dating sites (okcupid was one of them, and I thought that was probably the best one).
-Is it okay to see multiple people at once? Maybe that's a dumb question but I feel strange going on a date with a guy on Thursday and then out with a different guy Friday. One guy already seems to like me a LOT, and I'm not sure how to deal with it. I like him but we've only gone out twice. I need more time to know if I want to commit, but I don't want to lead him on or hurt him. Which leads to...
It's absolutely okay to see multiple people at once. It's a date, not a marriage commitment. Until you both have a discussion about being exclusive and your relationship expectations, you are free to see whoever you want. That doesn't mean you have to go on a date at every possible free evening if that's not what you want. It's all up to you. (as an aside, it doesn't sound like you're into this guy. Go with your gut.)
-How long did it take you to realize that you found someone you wanted to commit to?
I'm not really sure what you mean by this question. Are you talking about while actively online dating? I guess my experiences with online dating have been rather limited and I didn't go on many dates. So my answer doesn't really apply- my gf and I committed after our first visit (she lived far away at the time).
-How did you dress for second/third/fourth dates? First date I did kind of casual, jeans and a nice top. Should I go fancier for the next date if we're going out to dinner, or should I do about the same?
Depends where you're going. I think the rule of thumb is to wear whatever you feel good in. I don't remember adjusting my wardrobe according to which date it was.
-This is for the guys if one should stumble into this thread: How did you like girls dressing for dates? What's too casual/too dressed up?
I'm not a guy, but since I date girls I can try to answer this anyway

. I think it really depends on what you're doing. Too casual would definitely be sweats etc. Too dressed up would be something you would wear to a wedding (unless you're going somewhere that would require you to dress up, of course... and I probably wouldn't think much of someone overdressing, actually). It doesn't matter much to me what my date wears as long as she doesn't look like she rolled out of bed or was trying to pick up someone at the club (I think some guys might go for the latter, though, lol)