(Disclaimer: This is account is completely anecdotal - I have no firm evidence to back any of this up!)
I've just installed Windows 7 RC1 on my Lenovo T400 and have been going through the process of installing drivers / software etc (so far, so good!). It came time to install AV and although I have a license for Webroot's SpySweeper, after reading reports of incompatibilities with this and Windows 7 I thought it best to stick to the good old classic AVG Free which apparently is compatible.
One thing I've gotten into the practice of doing when installing AVG Free is doing a custom install and disabling the Search-Shield option, as I can't stand those pesky icons that appear next to every search result - not to mention the probable slow down as it goes to every site in the search list to check it's OK.
Once thing I had kept on was the Surf-Shield option - thinking that in this day and age a bit of added protection on links was probably not too bad.
So, having just installed all of this, I went back to the Lenovo driver download page (which happens to contain lots and lots of link) and had to sit there for about 30 seconds while it loaded the page. Having just been here 5 minutes ago and seeing it load in about 1 second, I knew something was up. Luckily the Surf-Shield option was fresh in my memory, so I went into the AVG control panel, disabled the option (it's under LinkScanner), went back to the driver page and it once again loaded almost instantly.
As I said, this is completely anecdotal, and I've done nothing other than above to test - but it does seem probably that AVG with the Surf-Shield option on could really slow a browser down(at least on pages that contain many links) with these two option on - needs some more scientific testing though!