"3) SW update (refresh) at home: Always use the latest N91 SW (currently 2.00). Like your PC Nokia is always issuing improvements and even new features sometimes (ex: WDRM came with 2.00 sw). The update process is simple and can be done here : www.nokia.co.uk/softwareupdate . This is a UK site however it has all the languages, operator and country variants for the world. Read the "phone sw update FAQ's" there. The updater will recognize the version of your N91 (country, operator) and look for the sw. If there is a new version it will tell you, if not then you have the option of reloading the current sw (ie if you wanted to start "fresh" again) or try later. Do not disconnect, answer/make phone calls etc during the process. It has worked well for thousands of people so far :). I suspect other sites in other languages will roll out eventually if you are uncomfortable doing the process in English. Also if you sw is not there it may be that your operator or country has not approved it yet. Keep trying. You can check you SW version by typing *#0000#.
4) HDD Users Guide : Nokia has now issued a HDD maintenance guide. Go to europe.nokia.com http://europe.nokia.com/A4158095 and select - Get support then from the list of phones select Nokia N91 there select User guides and from the list of languages select English. Then download the PDF. It has data about backing up and restoring (ie when to use PC suite and when no to), SW updates (goes through how to prepare for a sw update ), Themes and other TIPs. Alot of the tips from before seem to be in here. Also copying contacts to HDD has issues with 1.xx sw on GSM only China units (from Blogs), not on WCDMA units. Note WDRM rights will not be saved with a backup-restore (MSFT rules) but usually when you buy a song you get multiple synchs so it is usually not a problems."memory in use" for messaging (SMS, MMS). In addition to reducing battery life - its slow (HDD buffering is optimized for Video, Music playback), you have to switch back to the phone memory each time you want to use mass storage to connect to PC. In short why keep a bunch of messages on you phone anyhow?
...10) Gallery - When you have loaded new content via USB, after a sw update, hard resets, after removing the battery or the occasional reset the Gallery takes a while to open up (if you have alot of content it could be ~ 5-10 minutes). This is a one-off thing so be patient let it update its database and then after that it should be alot faster. The progress bar is a barber-pole thingy that does not give a very good indication (just spins). Be patient it has not crashed or hung-up just let it finish."
Full list here.