Then you're the perfect customer for the Z520i, I'd say. That is, if you like clamshells. I've had the T610 myself (my girlfriend still has one, too...), and I wasn't very content with the very same things you mention. Those things are really solved, I must say.
Maybe you can add other stuff, and I can tell you whether they're fixed and how.
Mind you: The basic functionality is still more or less the same. Animated menus are certainly nothing really to write home about, but overall, I'd say they took on the right things and made them better. Which is something that sadly is rarely seen in mobile phone "progress".
 

No, the lag's really gone. And the note on the Stand-By screen is really, really helpful, isn't it. ;) ... I guess personal preference is very important with mobile phones. That's why I think SE is doing good with enhancing the interface instead of replacing it with something new that has new problems.
On the other hand, there's this thought in the back of my head, that Apple could simply _rock_ the mobile phone world with an interface that's _actually_ good.