Generally I enjoy using N900, but these missing features I'd like to see fixed in future fw releases:
Major things:

• no search in email app, pain to find specific email
• no search in calendar
• Calendar view does not limit viewing hours (like working hours only)
• Maps does not support storing own locations
• Maps search required internet connection

Nice to have:

• "smart" birthday should understand age (and display it)
• Sync email/contacts/calendar with Thunderbird/Lightning
• Maps is slow to launch
• "SweetDreams" style time-based profiles, like turn of BT and ring tones during night time.
• Search content from PDF's docs etc.