YSlow analyzes web pages and tells you why they're slow based on the rules for high performance web sites. YSlow is a Firefox add-on integrated with the popular Firebug web development tool
This tool saved us so much time figuring out what our issues were. I highly suggest reading the rules. Also you can listen to a recent podcast from DotNetRocks: YSlow! Steve Souders finds Website Bottlenecks
So after removing the client side issues we realized we had a database load issue on certain pages with many records. Well we found out we ran into the famous ORM gotcha of way too many queries when using strictly the data objects with related foreign key objects. For instance, by relating a member record to the aspnet user table and doing a foreach on the member and then checking to see their username on the aspnet user table, it will cause another db query to get that info for each user. Sometimes when using the orm objects that are generated instead of writing a custom query to populate your own domain object, you can get into a lot of trouble.
Our website has many applications to it, some mvc and some using webforms. We have noticed a significant speed increase on the mvc sites. There is less code to render and there is no Viewstate so right away there is some performance increases.
I hope that this helps some other people figure out why their site is slow for some people some of the time.