stats collector spins my disk up every 500ms (8.2.3)

While looking for ways to get some more battery life from my laptop, I
noticed that one source of periodic disk writes was the postgres stats
collector process, which appears to write to pgstat.tmp every 500ms. I
could turn it off (in fact, for the moment I have), but I rather like
having working autovacuum ...

Questions:
1) this is on a system with I believe to be quiescent - there is only
one client open which is not doing anything. Before I get more involved
with this, can someone just confirm that pgstat will continue to update
this file even when nothing is happening? If not, then I guess
something /is/ happening and I need to investigate what it is (advice on
how to track it down is welcome - I already have statement logging on,
and there's nothing showing in there)

2) does the pgstat.stat file need to be preserved when postgres is not
running? i.e. could I move it to a tmpfs or something? I can see
nothing which suggests it has particularly important long-lived data

3) can anyone suggest a way to move the said file that doesn't involve
hacking postgresql source code? Not that I'm especially averse to using
a C compiler, but at the moment I'm using Debian packages and therefore
getting my packaging "for free", as it were.

4) if no answer to (3), what would be a sensible approach? First I
thought it should probably be an option for postgresql.conf, but now I
wonder if it should just be hardcoded to the same directory where the
unix domain socket and the pid file live - they being similarly
transient data.

If this isn't the right mailing list for these questions (I think it
probably is for 1-3 and not for 4 ...) please feel free to move it.

Thanks

-dan