I've upgraded my iMac to Tiger as well but have had a better experience. Sure OSX seems to load faster and Dashboard is cool/handy, but spotlight has been my favourite feature for many years in computing. I don't have to fiddle around with Finder to launch an app or file hidden deep within my HD (you know... /Applications).
For me Spotlight works very well especially with Finder's shortcomings.
But I guess in the end all of the Tiger features that were advertised are not really necessary. They simply make things quicker to do I guess.
Also, Safari RSS and Mail are quite good. Mail has now replaced Thunderbird as my email app (Though I'm not sure if you can import Thunderbird mailboxes
).
Unlike
tommelbourne, Tiger hasn't been less stable than 10.3.9 for me but I use my iMac for very simple uses - surfing, email, iCal/Address Book, iLife, Word, QuickTime/VLC, bittorrent, iTunes... you get the idea. No Logic or Photoshop or anything. So I can't comment on Tiger's stability with large apps.
I'm only fairly new to Macs, but am I right in saying that Tiger's best new features are mainly under-the-bonnet, supposedly to be used by future apps?