GDI
Basic Windows code is all internal, the GDI is only really there for doing things such as drawing stuff, and by drawing stuff I mean like what you would see if you started drawing stuff in Paint. It can be used for more complex stuff, but anyone who does is not doing their users any favour, or themselves. It is significantly easier to code the same effects in OpenGL or DirectX, and it will run significantly faster. Ever since the mid 90s when 3D cards started becoming standard, GDI was doomed. Slowing down GDI will be very unlikely to slow down any apps you run at all significantly (and shouldn't slow them down to the point you can notice them slowing). There will be a small slowdown.
@alistair millington
As stated COUNTLESS times before, Vista uses RAM as it is freed. You can no longer estimate how much RAM is being used, as Vista makes as much use out of RAM as possible. It will fill it up if it can, and then decache stuff when you need the RAM for other stuff.
When '95 came out everyone screamed about it for using up too many resources, then after a few months people started working out that it was actually not bad at all.
During XP's lifespan it got slated for being insecure, needing a reboot too often, BSODs.
Vista comes out, everyone screams because it needs a better PC than XP, even though it fixes the above problems with XP.
Also, my install works fine with my home and company networks.