I don't think this is an isolated problem, as a quick search of various compatibility forums turned up a few similar cases (RIFT was one). In my case, starting a Steam game (Oblivion) at fullscreen 1280x800 brings up the game as normal, except that the OSX menu bar is visible. My native laptop resolution is also 1280x800.
The strange thing is, the video doesn't appear to be squashed. I had a similar issue with Mount & Blade Warband, but the window was lacking in focus, and after a bit of tinkering and clicking the window to ensure focus, it has since had no issues.
Tinkering and setting Oblivion in winecfg to use the same sort of settings as Warband has not yielded any results, however. I have tried various winecfg settings: disabling the window manager decorations, disabling window manager control, disabling virtual desktop (which I had set to 1280x800). Disabling all three. Trying each by themselves. Enabling all. No combination appears to have any difference. Some combinations, however, seem to make it impossible to skip the company logos startup videos--only when the main menu appears can I use 'escape.' Another oddity is that it appears to behave as it is in fullscreen: trying to point my cursor out of the game window, to the menu bar is impossible. The cursor will not leave the edge between the game screen and the menu bar, even though the setting to prevent the mouse from leaving the window is unchecked. CMD+F or CMD+Enter, which tend to be fullscreen/windowed toggles, do nothing to change the window.
Any ideas on a fix or if this is an isolated issue?
My specs, should they be necessary, are as follows:
Late 2009(?) Aluminum Unibody Macbook
Mac OSX 10.6.8
2 GHz Intel Core 2 Duo
2GB 1067MHz DDR3
Nvidia GeForce 9400M