-Non pirated versions have the product activation.

-XP dual boots with Linux like a bitch on some systems(such as mine). Previous windows work happyily with Linux.

-Some systems have major problems with it out of the box.

-There is some form of spyware from Microsoft in it, a firewall SHOULD pickup some wierd outgoing transmissions.

-Even wind0ze XP will start to cough eventually after a few months on some systems.

-It's 0ld$k00l compatibility is a joke.

-It's scaled for more modern systems, scaled to encourage people to jump back on the upgrade rat cycle. Wind0ze 95 can run really slowly on a 386, Wind0ze XP does warrant a faster system, but it seems too much of an upgrade for what it gives.

-It's the beginings of Palladium, DRM, and TCPA.

-The possiblity of blacklisted copies being "bombed" by MS. I am not sure how that works though, I belive my XP is blacklisted, but so far I think it just means I can't use windows update.

-The pervasive EULA that is blindingly agreed to, a EULA that can allow MS new powers over you that they haven't overly exercised yet.

-The semi-theroetical "crap out" theory. In W98 and some others wind0ze, MS may designed a crap out mechanism, making the Wind0ze perform very slowly and unstably after two years. XP may have this mechanism. It can only be solved be a re-install. W95 is so old, that MS did not put such a thing in it.