Apparently software rendering on Saucy

[Colin Law]

I have Saucy installed on a laptop with Intel 9845 graphics.  It is
incredibly slow rendering Unity related stuff.  For example when I
hover over the launcher it takes several seconds to show the popup
hint for each launcher, and the popup appears in several steps getting
darker each time.  This suggests to me that it is using software
rendering.  However, when I run
/usr/lib/nux/unity_support_test -p
it shows yes for everything, so I don't understand what is going on.
If I run top whilst doing unity related stuff then I see that compiz
is hogging the processor.

I can't see anything relevant in syslog, Xorg0.log or .xsession-errors.

Has anyone any suggestions where I might look for clues before reporting a bug?

Colin