We've been looking into what could be the cause of the GPU2 upload issues people have seen. We have some ideas and that has resulted in new server code and a new client. The new server code has been tested on vsp07 and is now rolled out on the other GPU2 servers (vspg1, vspg4v2, vspg3v2) and we're monitoring it.
The new client (dubbed 6.20r1) is now undergoing closed beta testing. If that checks out, we'll release it for open testing. The new client is the key part of this fix (new client + old server code is probably ok), but the new server code will help a little.
Also, the new server code is useful for the stats change over (described below, where we separate out NVIDIA from ATI stats). Note that the osstats page will be screwy for a while during this switchover.