To me IE7 has simply added some of the better features of the existing Opera and Mozilla browsers.
However, like Media Player 11, IE 7 has changed some of the more standard features for the worse. I only ever use Explorer for the Bulletin on Football365.com - if you have ever seen this you will know why - so the security issues are not that much of a concern from that point of view. All my banking and buying are done through one of the other previously mentioned browsers.
I did install IE7 but it drove my Spybot insane as it was forever looking on to the internet by itself, so I re-installed IE 6 and calm was restored in the land of my virus and spyware protection.