Ive been using Pro 11 64-bit and have been running into many issues that V.10 did not produce.
1) Crashes all the time doing lots of various editing tasks.
2) Every time I load a project it has to rebuild the audio tracks. (This may be a setting that I changed) I don't know. Takes over 10 minutes on some projects.
3) Sometimes the FX window will freeze, but everything else seems to be OK. I have to restart Vegas to fix this.
4) When rendering, only around 40 to 50% of my ram gets used and the CPU is running around the same. Render seems to be slower since the upgrade.