-What exclusives do you enjoy the most on the PS3?
Gran Turismo and Ratchet and Clank are the two Sony exclusives that I would really miss if I didn't have a PS3, but I have a 360 as well so I'm not really forced to choose. That said, I never had the original Xbox, but I have scads of PS1 and PS2 titles, and since I bought my PS3 early, it still has backwards compatibility with basically everything. Granted, I almost never take advantage of that, but occasionally we like to have old school gaming nights at my house, and it's nice knowing I can fire up Twisted Metal 2 or Grand Theft Auto III and have it work.
-How are the media server capabilities?
I like them better than the Xbox 360, honestly. The PS3 integrates with Windows Media Center as well as the Xbox 360 (although it's a bit slim on codecs), and the Netflix UI is simple and intuitive. Outside of Netflix, I don't use either for much streaming, but the Xbox 360 does have the edge when it comes to letting you stream your own music during a game over a media server.
-Blu-ray. Come on, do you really use it?
Absolutely. It's actually the principal reason I bought the PS3 over the 360 when they launched. My roommate and I have around 500 Blu-rays between us, and a couple hundred more DVDs. The PS3 is better on every front than the Xbox 360 in playing physical disc media, from the upstreaming of DVDs to Blu-ray (which the Xbox 360 doesn't have; sure, you might be able to find an HD-DVD drive for it, but since they haven't made any new ones in years, you're going to have a severe lack of media). As something of a videophile, I'm biased in this area, but HD streaming cannot come close to Blu-ray at this point; what's the point of a giant TV with an excellent picture if you're just using it to display a sub-par source?
-FOR THOSE OF YOU WITH BOTH SYSTEMS: Which do you use more and why?
For media use, the PS3, hands down. Actually, I don't know that I've ever used the Xbox 360 for media (outside of music, and that's primarily streaming while playing a game). For gaming, it honestly depends on what's been recently released. I'm not a big console gamer any more, but Forza 4 just came out and I've been playing that heavily for the past month. My roommate has been playing a lot of Fallout 3 on the 360, but he also just got Heavy Rain for the PS3. I bought GTAIV on the PS3, but I got Red Dead Redemption on the 360 because of the image quality issues which were hotly debated on the internet. Generally, if I start a series on one machine, it makes sense to continue it on the same machine, since some games will give you perks for having previous save files. Ultimately, they're both on par with each other, and it probably comes down to exclusives. For me personally, the Blu-ray is the dealbreaker if I had to pick only one, but if you don't care about that, then I suppose it won't factor into your decision.
One thing I will add (although it sounds like this probably won't affect you): Transferring saves between systems. When I moved in with my roommate, we each had both systems; consequently, we now have two Xbox 360s and two PS3s in our house. When I was playing Gran Turismo 5 earlier this year, I could copy my save game onto a thumb drive and transfer it between systems in seconds; if he wanted to use the main TV, I could go up to the TV in my room and still make progress in my saved game. Piece of cake.
You would think the Xbox 360 would be just as easy, being that it's built by a company that specializes in PCs. Not so. When I tried to port my Forza 3 save over from his Xbox 360 to mine, everything got erased. I had a Level 50 driver profile and a number of livery paints and decals which I had spent dozens of hours on; all told, I probably lost 100 hours of progress or so. And it wasn't just my Forza 3 profile, it was all my games (fortunately I had only played a couple by that point, but I did lose all my GTA: Episodes From Liberty City progress as well). That was a giant pain in the ass, and it effectively means I will never try it again; I don't want to go through that hassle again. Which means that if my roommates are using the main TV, I can't play any 360 games on my profile without physically moving the machine (not worth it to try and disconnect it from the entertainment center). That's a huge red flag to me, but, again, since you probably won't be transferring saves between multiple machines, it probably doesn't affect you.
Overall, I use the PS3 more, but that's because our household is definitely more about watching media than gaming. For gaming, I would say you can't go wrong with either system. I like the Move more than the Kinect, but there's not any software out for either that I would say is a must-have title, and neither is really worth it at the moment. Ultimately, I'd say get the PS3 and keep the 360; I don't see a reason to get rid of one just because you get the other.