Please take note that an OTA (over the air) update does not always work simply because of the verify situation and can leave your N900 in a reboot loop or a refusal to start up DON'T PANIC you cannot do any damage whatsoever to your device either by OTA or flashing manually and something goes wrong.
The way forward from these kind of situations is to just take your time and do a manual flash again if need be untill the N900 accepts the flash and starts up normally.
If ever you get slow reactions from the N900 after it reboots itself from being flashed, simply wait till it has done the cycle of rebooting and turn off and back on again.
To get back your apps after a successful flash simply do a restore from the backup you did prior to flashing follow the prompts and it will re-install all your apps automatically.
It is actually IMPOSSIBLE to "brick" the N900 from flashing in any way or form please remember this.
All faulty for whatever reason flashing can be done again with no ill effect whatsoever to your N900 and as many times as you want or need to flash.