Henrik,
> I tested it, and it doesn't seem to change significantly
>
> Now I am trying the more regular vacuuming, too ... every 5 minutes
> the most important tables are vacuumed... this, too, gives a bit
> more performance.
Disregard that last message. I just caught up with the list.
If you're VACUUMing constantly, then another setting you may want to
tweak is vacuum_mem. Like the other memory settings, you're looking
for the "sweet spot" where vacuum_mem is high enough that your vacuums
are over quickly, but low enough that it doesn't take away memory from
other processes and slow them down.
It may be that you don't need to change the value at all. I would,
however, try increasing and decreasing my vacuum_mem to find the level
at which the frequent vacuums have the greatest benefit.
-Josh Berkus