Okay this is basically copying Daniel Rutter's blog post on the subject but I consider both to be worthy of me posting about as well.
Firstly we have Microsoft decided that after paying a small fortune (£190 for Vista Home Premium - the non-useless Home version - and £325 for Vista Ultimate - the version with Remote Desktop server enabled) for Vista in the first place, you'll only be able to upgrade your computer once, and on your second upgrade you have to buy another copy of Vista.
Firstly we have Microsoft decided that after paying a small fortune (£190 for Vista Home Premium - the non-useless Home version - and £325 for Vista Ultimate - the version with Remote Desktop server enabled) for Vista in the first place, you'll only be able to upgrade your computer once, and on your second upgrade you have to buy another copy of Vista.