I use HTC X-Button for this:
http://forum.xda-developers.com/showthread.php?t=283658
You install it, then configure it under settings and you can set it up so clicking on x closes the app or holding x closes the app.
And no, there's no way to fix the memory management. Nobody has cracked the key to overclocking the processor either. The dual-core architecture is too new at this point.