SuperPreview is disappointing, IMHO. It shows screenshots of the various browser's renderings, but they aren't interactive. Since a lot of cross-browser bugs are JS related that doesn't really help.

Xenocode's browser sandbox on the other hand is great: http://www.xenocode.com/Browsers/

It lets you run all versions of IE, Opera, Firefox, and Safari without having to install them. They were also sharp and included the IE Developer Toolbar in the packages. Highly recommended.

I think that the browser sandbox and SuperPreview serve different purposes. The sandbox will allow you to do the js checking, but SuperPreview allows you to look more at design elements through overlay and rulers. This is the same feature provided in Adobe browserlab (mentioned in another comment), but browserlab is currently closed to new users.

I really wanted to like this, and didn't mind the 250MB download, because I just got my coffee while it was downloading. But the first address I entered caused an error page about insufficient memory even though my system shows 800MB of free memory. It has a nice bug report facility, but wanted me to signup for Microsoft Connect in order to leave feedback. Which I did because I want this product to succeed. So a big "meh" overall on this one at this point.

I was about to download it, but 250MB? That is more than the total size of all the browsers it supports!

Of course it's going to be bigger than all the browsers combined. They have to include all the browsers plus extra software to contrast and compare the output.

If it offered a real-time html/css editing facility for any browser it contained akin to firebug, I'd be a happy boy.

It's interesting that Adobe brought this out a few months later - https://browserlab.adobe.com/index.html

It looks quite useful, and it fills in a huge gap in the market.

The gui could use a bit of clean up though.