I have no idea whether these are Windows specific iTunes hate or whether they span the platforms but I only have experience with iTunes on Windows so I'll restrict it to that. Feel free to chip in and complain about the Mac version later.
I'm not entirely sure why people rave about iTunes - I suspect it'shte iPod and ITMS integration but people raved about it before then. Maybe they were blinded by the shiny metal. Either way, I have no iPod (HERECY!) nor the inclination to by DRM encrusted tat from iTMS so I miss out on those benefits. Ooh - I can organise my podCasts . Which would be great. If I listened to any. Aren't we supposed to call them soundBlogs or something now anyway? However, the single biggest hate I have so far is why the auto complete in the ID3 field editor. Here's how to replicate the hate ... 1) Obtain mp3 from somewhere 2) Realise that ID3 tag, whilst technically correct, is lowercased 3) Try and edit that 4) Have iTunes know better than you do and autocomplete the field back to the lowercase version 5) Try again 6) Have same experience 7) Scream. Curse. Rant. 8) Edit the field to say "Foo" 9) Rename it back to Properly Capsed Version of Name 10) Repeat with other MP3s 11) See 7