Tools like National’s (now TI) WebBENCH have allowed engineers to design power supplies without downloading any software for quite some time. Recently I got an account at Upverter.com. This web application is focused schematic capture with social sharing.
Just announced this week, Digi-Key is looking to enter this area with their new web based tool to share schematics, Scheme-It(sm).
I haven’t had a chance to put it through its paces yet, but I look forward to comparing to Upverter and Eagle version 6 soon.