I always install only one or two apps max at a time - especially if they are still being tested. That way I can uninstall that app straight away if the
N900 starts playing up. It is amazing how many apps make the N900 do weird things.
If you went an installed 20 apps at once, you would never know which one caused the issue and more than likely you would have at least one issue.

I believe this is the root (excuse the pun) problem of many of the complaints out there with regards to performance. (apart from the bugs that are well known to be in the OS itself)

It seems at least 90% of the users out there have a phone/computer that works fine (I am one of them)
A lot of people have issues, but are aware they may have caused them.
There are a certain number of niggly bugs that came with the phone or with PR1.2 (like the answer button moving when trying to answer a call)

I don't complain about things, because I realise that it does nearly everything and more than was advertised.