Oh! Glad finally someone asked. The front-end's using flash w/ as3. It was the 2nd project I made using flash, so it was really exciting when I was scrambling across the web for resources. The original front-end the client was actually layering each stroke on top of each other, so what ended up happening was the client would crash after 20ish minutes of moderate use. So I fixed that and ended up using bitmapping to handle the screen. I had a bunch of other features that I disabled for this release [opacity and the undo function] just because they were too buggy.

The server's running I believe CentOS 5.6? or .7? And it's written in Java. Anywho when there's incoming information it stores the coordinates that are being drawn into a buffer. If the buffer becomes full then it shoots it out those coordinates. There's also a 50ms cycle that checks the size of the buffer, so even if it's not full, it'll shoot out the points.

-edit-

I mean, for now the server architecture can handle light load but I definitely plan on implementing a more scalable solution if I get more traffic.