I was lucky enough to arrive at the store where I had pre-ordered my APC40 on Saturday and actually have a unit there waiting (sounds like some people weren't so lucky which sucks).
Unfortunately when I got home and set the thing up it was acting unbelievebly strange, the second it was configured in Live's (version 8.03) midi devices the APC just started royaly freaking out. Random lights started blinking frantically all over it and it just kept sending an immense amount of midi signals to the application and switcing random clips and scenes on and off before locking things up.
I spent a few hours tooling around with the driver (based on the whole confusion over 'USB Audio Interface', a Microsoft 2001 generic driver on XP SP 3 binding in to control the device). I now see a lot of posts with people referring similar confusion over this and a reg hack to potentially give a more logical name.
I removed, readded, reservice packed, opened a call with both Ableton and Akai, and after two hours had achieved nothing more than frustration.
In the end I trooped back down to the store and insisted they swap out the device (something they were less than eager to do as the things are moving fast). Took the new one home, plugged it in and presto....works to perfection.
Just a heads up, if your APC starts firing random messages in fast succession the second it is enabled in Ableton it's dodgy hardware straight out of the factory, save yourself all the time I spent troubleshooting and just get it swapped out.
All that aside, for Ableton users this is an absolute gem of a unit...it's almost like going from cursor keys to a mouse in computer history terms....
Cheers