I find it a lot quicker to start than IE7, which is a good improvement.

One of the major changes, under the hood, is that IE8 uses standards-compliant mode by default, which means it renders pages correctly as per the various web specifications.

The downside of this is that over the years many sites are adapted to previous versions of IE's 'quirks' and so can look a bit broken in IE8. A quick way to fix this is to turn on 'compatibility mode' on a page-by-page basis when you see problems. this makes pages render like IE7.