I love my n900 but now i have a lot of problem with that

my dropbox stop to synchronization,
sometimes the zim-wiki(the best Program ever) it sometime crash
and the main problem is the n900 is really slow.

What you do to maintain your n900 as your main Phone?

i don't really want to change my n900 phone, i love the keyboard, i love that i can change everything, i love that the dropbox is download the file to the phone, i love the FM Transmitter, i love that when my hand are wet i just can take everything to stop the alarm.

http://wiki.maemo.org/N900_The_Perfect_Setup

Use the above guide to clean up your phone.
Limit the amount of applications you install (especially widgets).

Also many people find CSSU-Thumb can help if you don't mind using CSSU-Testing.
http://talk.maemo.org/showthread.php?t=84829

All of the above. And something is to be said for running swap on a SD card and deploying one or other of the swap changing strategies. Particularly if you are a heavy multi-tasker...