If you really use Voice Search and Voice Activities then this is the best phone.
My last device was an Eris which, even if I had only a couple of apps loaded, became so unresponsive as to become unusable (e.g. 20 sec for a call to begin after pressing a "Favorite" on the home screen.) My wife has a 'Fascinate and I like the large S. AMOLED screen. I really wanted a 4.3" screen but thought I might hold out for the thinner, lighter Samsung Stealth. I don't really watch long videos or download tons of media (though I do need flash for checking video surf reports) so I didn't necessarily think I needed 4G. On the other hand, I really like HTC Sense. So, the decision was between a fatter, heavier, TB or a lighter/thinner Stealth when it comes out. While in the store, I tested web page downloads/render speeds between the TB and the Droid X and found no noticable difference (though 4G was not available in that area).
However, I also tested Voice Search and Voice Actions responsiveness between the Fascinate, Droid X and ThunderBolt. For me, voice search on the Fascinate is quite slow and innaccurate. On the Droid X it was moderately fast but quite accurate. On the ThunderBolt it is extremely fast (both in terms of starting up as well as in returning results) and quite accurate. This is already drastically improving my smartphone experience.