Steam has it's shares of issues:
Updates/downloads saying they're downloading but not doing so ( until you click launch game then it starts doing something).
Cancel buttons not working in most window popups. ( While I can't recreate the issue tm, I'm positive this happened to me often)
Steam windows being unresponsive when launching a game. ( While I can't recreate the issue tm, I'm positive this happened to me often).
STCC - The Game Demo not wanting to disappear from my game list even after manually trying to remove it and normally removing it, it shows as download paused no matter what I do.
Steam itself sometimes freezing/becoming unresponsive ( often happens when you've just bought a new game and it's ''preparing the files for install''...
Says fragmentation is 0% on particular game files, but when I run a defraggler analysis it shows otherwise, just about after every update tf2 files are fragmented...
But, It beats any setup &cd/dvd/brd based rubbish, I far prefer buying games on steam than retail games. CBA with optical media any more, I hope it dies as soon as possible. Changing a cd/dvd is enough reason for me not to want to play a game any more.