GPS Status is a free utility that I find handy to make sure the GPS is working properly on my Android devices. On my old LG Ally I could open GPS Status to get the GPS to lock more quickly, then close it and switch to Navigation. If I did not do that, Navigation migth take several minutes for its GPS to lock and sometimes never lock at all. GPS status is in itself a GPS app in that you get a display similar to a hand held GPS unit, but only the real time data, no waypoints or mapping or anything like that.
Is your A500 by any chance rooted? If so there is much more you can do to help the stock GPS in the tablet. The folks over on XDA Developers have an app that fixes a lot of the shortcomings of the stock GPS software to make it lock in extremely fast and be more stable. They also have a post explaining the gist of what they had to do and why. It seems Acer used some very generic and imprecise software in the tablet's GPS feature. Their utility corrects these issues. It made quite a difference on my A500, even indoors.
Read this thread if you are interested:
androidforums.com/iconia-tab-a500-all-things-root/475551-gps-fix.html