Upload size is ultimately limited by memory allocation, and other configuration factors (e.g. 32bit vs. 64bit architecture, OS, etc.).
I've managed to upload ~250MB on a 64bit Win7 machine with ~1GB allocated to the JVM.
If you must upload larger files, you'll have to try other configurations, but again there will always be some limit with the current implementation.
My experience is that allocating ~2GB on a Windows 64bit machine with 8GB RAM, is possible. You should be able to allocate even more on the same machine running Linux.
For best results, use the Firefox browser..