If you find Gmail and Twitter equally useful, and would like to integrate both together inside one interface so you can follow both feeds quickly and easily without the hassle of jumping from one application  to another, then Twitter Gadget for Gmail might be the solution you are looking for.

This gadget basically put a twitter feed "banner" inside your gmail interface (see picture). By having such, now you can quickly access your gmail account as normal, yet if you want to make a twitter update, or catch latest twitter feed quickly and easily, you can do such from inside gmail itself; no need to switch from one application to another.

Here's the URL where you can get the gadget: http://twittergadget.appspot.com/

And here's step by step help instruction, of how you can install the gadget into your gmail account: http://blog.go2web20.net/2008/10/how-to-add-gadgets-to-your-gmail.html

Hopefully you find it effective, and pretty useful too.