I was watching a very interesting video from MIX11 which deals with optimizing website performance using ASP.NET. A lot of the tips are general to web development, and not just ASP.NET, so I think it's worth watching for anyone. If you don't feel like watching it, then at least just check out the below: - Yahoo's YSlow Plugin - Google's Page Speed Plugin - Best Practices for Speeding Up Your Web Site, from Yahoo - Page Speed Family, from Google (look for the 'Page Speed rules' menu)
So try them today, and don't worry about getting 100%, but try get to at least 90% - even small things like ensuring GZIP compression is turned on will make a noticeable difference.
There is also a mod_pagespeed Apache module from Google Page Speed which can do automatic optimizations, I haven't tried that, nor would I really be confident in trying it just because I'm a control freak, but it is from Google so it probably just works. If anyone has used it successfully, please let me know.