(i) No Cut function in Finder.
(ii) Frequently crashing finder in Leopard.
(iii) Bad Trash management - I want to be able to free up space on a USB thumb drive without having to empty Trash on my startup drive!!!
(iv) nonfunctional features that were nevertheless widely touted as breakthroughs. Spotlight in Tiger is useless (try to search for a phrase - good luck) and gaining the functionality requires a paid upgrade. This is not a new feature, for which I am paying, but merely a bug fix. Granted, 10.5 has many useful features, but I am only talking about spotlight.
(v) networking in OS X was not functional before 10.5. Again, gaining a basic functionality, which should have been provided as a free update for Tiger, requires a paid upgrade.
(vi) Quicktime player by default throws some idiotic popup advertisements at you when all you wanted to do is to watch a clip from a web. Often, Quicktime can not play the clip but still promptly shows me the popup. This behavior is obnoxious and mirrors the worst of Windows.
(vii) Office for Mac is slower than that for PC. To be fair, the new Office 2007 in Windows has approached the sluggishness of Office 2004 that Mac users have "enjoyed" for years.
That's about it, more or less. I could make a much longer list for Windows annoyances, if asked to.