>For anyone who's using IE7, what is your opinion of it? (compared to IE6).

I find that I don't use tabs at all. Things I like:
- printing: it finally works and you can squeeze everything onto 1 page is a reasonable way
- zooming: you can zoom a page, both text and graphics just like you can do in other MS apps. Great for really small or really large screens

We've had zero incompatibility problems with our main browser app.

>I got around to installing it last week - functionality is nice, especially the tabs, but I'm disappointed in the performance.
>Have others run into problems with IE7 being sluggish?

It is certainly slower that IE6, but I find that on both my systems IE7 is faster than Firefox 2.X