Skinning Gmail with a Custom Stylesheet
This is damn cool. Consider the possibilities if you will: personally I like the minimalistic appearance of Gmail as it stands. But, the key improvement I would really like to make/see would be to remove the targeted advertising in the side panel. Using CSS, it would be quite possible to eliminate these ads by simply adding: ( display: none; ) in it’s associated div, and Whoila! …no more advertisements in Gmail. Once I get some time I will actually sit down and play with this and see if I can do just that. Check back soon and I may just have this little problem fixed. 
Wandering the Interwebs 