How can I connect my A500 to an iMac for charging and file transfers? I have a Acer Iconia A500 and I am using an iMac. I cannot charge or share my device as mass storage with my computer over USB, though I am able to use bluetooth for transferring data.

Are there any special drivers needed? How can I get it connected with my machine?
As eldarerathis mentioned, you need to charge the tablet using the charging adapter rather than USB.

The A500 has 2 USB ports.  A regular one, like you'd find on a laptop, for connecting USB devices to the tablet (memory sticks, for example), and a Micro USB port for connecting the tablet to a computer.  Make sure you're using the Micro USB port.

(Your mileage may still vary - the support site isn't very forthcoming on using the tablet with a Mac)