Textmate is Cocoa right? I'd be useful if they could produce a web version with cappuccino. It'd be great to fire up a browser, point Textmate.com to my Github repository, and work.
I would love to see it happen though, along with the ability to easily pair on a codebase via the browser, like Bespin is trying to do.
That said, perhaps it just needs a Gears-like ability to work in a disconnected state.
Like sharepoint, but without the destroy-file-on-save feature it triggers when you save against it in gvim in some circumstances. Doing it via git integration could be a great way to achieve this without rebuilding the world.
Could be achieved via a FUSE filesystem wrapper on linux workstations.
Right click a project in Eclipse on your Core 2 Duo, and time how long it waits for the context menu to show up. Then right click any other IDE, text editor, or non-Java app, and attempt to do the same.