it looks like you had the exact same issue I had a few weeks ago. Basically the latest GMA 500 drivers are rubbish and run at a crippling rate. I actually went as far as accessing the Intel's Embedded Graphics Drivers and compiling my own version of their latest gold drivers. There was certainly a marked performance.
However, at the time I was trying to use OpenGL 2. Even though Intel state that the GMA 500 can use OpenGL 2 their drivers do not (though I have no idea why they have done this). After much prodding and poking with the various drivers there was too much going wrong with the embedded drivers.
I ended up reinstalling the latest public release drivers but found the graphics speed so crippled on the laptop that I basically gave up and took the laptop back to the shop. I am sad to say that though the Acer was in principal a really nice laptop Intel have really let it down by providing sub standard drivers for their technology.