Well, in July I was tossing up between the 17inch dell and MBP, and decided that the latter would be a nice change. (although the price difference with education discounts was $1500 between the two). Early this month, I got my sister the dell I was planning on buying for her 21st (which has exactly the same specs, but with 3Gb ram instead of my 2gb).
Personally, I cannot see a difference when it comes to playing games (with bootcamp), though the mac version of games might be a touch slower. Aside from this, my mac is thinner, smaller, lighter, boots up the OS in 30 seconds (shuts down in 10-20s) (as opposed to around 2min with dell), is awesome for uni assignments and presentations (if you have iwork), is easy to transport, small power adapter, and crashes very rarely, has a giant trackpad that is more logical to use (two finger scrolling etc), doesnt have an exhaust vent blowing hot air into whatever may be sitting next to your compouter (possibly uncomfortable for lefties), has really good speakers, backlit keyboard, and has that awesome remote..
Downside; expensive, if the charger is not grounded my mac lightly electrecutes my forearm after a while, playing games for too long (5+ hours day after day) makes my wrists ache, sometimes freezes while watchin some DVDs (the movie keeps playing, just cant adjust volume etc), after using OSx using vista does not look so attractive, people will try to argue that macs suck, you will fall in love with it.
If I went back in time, and was to choose between a desktop gaming PC and this MBP, I still would stick with my MBP.
N.B. I've always been a hardcore gamer, and I am very happy =)