Hi,

ASP.NET 3.5 SP1 has browsing history (making bookmarking functional too) handling support built in.
Resently web applications become more and more ajax-style, it is important to keep that in mind and see where it is reasonable for use.

You can read about it here:http://msdn.microsoft.com/en-us/magazine/cc972638.aspx

It is a very recommended article for ASP.NET developers to read in general, It also reveals the ASP.NET v4.0 Ajax Template approach, looks really cool.