I think the Ctrl-Tab functionality could be improved. Currently, it cycles through parts which is fine if you just have a few open. However if you have a bunch, it basically becomes useless...
A better solution would be that Ctrl-Tab cycles between the two most recently used files. Therefore, you can go from Assembly to Part and back to Assembly extremely quickly. Additionally, the third most recent would be two Ctrl-Tabs, fourth most recent would be three Ctrl-Tabs. Lastly, if you held Ctrl-Tab it would bring up a grid with the thumbnails. This would allow you to find a part by its physical appearance rather than it's PN (which are non-descriptive at my company).
Basically, this whole system would function in the exact same way that Alt-Tab works in Windows.