Just finished reading the changes brought with XP2 and there are quite a few. Those of you who understand French, you can read it for yourself at www.clubic.com.
This new SP was designed mostly to improve security and stop the viruses spreading. They did a good job of it by implementing different measures and a better firewall. This has its drawback. They have DEP (Data Execution Prevention). This function is also implemented for the 64 Bit and future Pentium E. This Nx Bit feature (No Execute) allows forceful shutdown of unsollicited code execution in memory. Sounds good in theory but in practice, the tests they performed, this process killed programs such as Adobe Acrobat 6, Pinnacle Studio 9, Ulead DVD MovieFactory 3, PaintShop Pro 8 etc... It even closed MS programs.... It is very tempting to disable this function.
Antivirus wise, again they focused on security. You have multiple side panels which will tell you that this page attempted downloads etc.... You know, those automatic downloads you get. Well, XP seems to think that they are all viruses because it blocks them all and you have to manually set it for download thereafter. Once that is done, you still have another pop-up telling you that it is a risky business.... How much is too much. Again, you might be tempted to turn this process off.
Another biggy, at least for a gamer such as I.... SP2 is very very resource intensive. Where the SP1 could accomodate itself of 256 GB of RAM, this one needs 512 to operate well enough. Even then, they noticed a 5 fps drop in FarCry, no matter the resolution.
The report goes on and on and covers everything from blue tooth support to drivers etc... I suggest you find similar reports and read a bit before downloading it (whenever the toned down version becomes available). It is indeed a lot safer but it might take a while for you to get used to it and customize it the way you like.