Well, not just GZ but websites in general. Whereas with Opera 9.1.0 pages load really fast, IE7 on Vista takes a dog's age. No AV, no firewall, no phishing filter enabled.
I think it may be related to Javascript, as the slowness is particularly noticeable when loading the TinyMCE editor for instance - the text area loads fast, but the controls can take up to a minute to appear. Same when you create a new blog page, or comment on blogs.
IE7 under XP is very fast indeed in comparison, ditto Firefox.