I'm using the IE 7 beta, and I really like it.

I have found it to have a faster startup than Firefox, and has the tabbed browsing. It took a bit (day or so) to get used to the differences IE7 has over IE6.

I grabbed the Beta at work because I needed to test some stuff, and it didn't take me long to want to have it at home too, though it only works on my desktop - I can't seem to get it to install on my almost-4 year old laptop.