The Tyros2 with optional HD, and the PSR-S900 with a USB flashdrive can capture a recording, including vocals(or even another keyboard or instrument plugged into it) but it is not "on" all the time.

I vaguely remember a buddy of mine having an Ensoniq keyboard that had this feature, although it wasn't an arranger.

Might be useful...but a good editing system would be important to have with it.

Ian