Ha ha,

Typical!
The evening after I posted about my successful sl build, I got home and it wasn't working properly.
Sound had vanished again (couldn't get it back for some reason. And every 1 in three restarts would bring up a blank blue screen instead of the desktop. The only way to bring the desktop up bing to swith the machine of and on again real fast (bringing it back before it has the chance to actually power down.

I did use the migration tool to copy across some programs and files. This seems to have been the cause of it all. Perhaps because the 2 machines were on different releases of sl (10.6.0 and 10.6.3).
Doh. Back to the drawing board.