This one's more of a pain, because it requires an exit from Vegas.
About once a day, when I zoom all the way out of the timeline, I can no longer zoom back in. The project plays fine, but when I use the + and - buttons that are below the timeline, nothing happens.
I've had this too and it is annoying. I don't know what's up but there's a way to "fix" the stalled zoom without exiting and get it going again. Grab the vertical bar between the "+" and "-" buttons. The cursor will change from the standard pointer to a vertical bar with two arrows pointing left and right. Click on this hold and move the mouse left to zoom in (+) and right to zoom out (-).
This resets the freeze and you don't need to exit Vegas.
I've had this too, and assumed it was something with the mousewheel wheel-driver on my new mouse. It seems to fix itself after 30 seconds or so, but comes back later when you least expect/want it. But yes, it affects keyboard up/downkey zooming too. Has it been 'officially' submitted as a bug ?by anyone yet