Well I just installed tiger and think its a good update,(not sure though if it was worth the 129 euros..) But besides spotlight, automator and dashboard, theres really lot of other things going on underthehood and makes tiger the most stable and best mac os yet. and unlike windows updates, mac os updates always have made the computers run quicker, something that never happens in the world of windows...
For nice review of tiger:
http://arstechnica.com/reviews/os/macosx-10.4.ars/1