Polls are fun, but to me, neither of the above is the answer.
The reason why Rainlendar is such a success with yours truly, is the fact that it respects my data. I move around between OS and apps all the time, and I basically want my data to be accessible everywhere. I can use Rainlendar with XP with Linux, and I can still mostly see my data with other applications (such as Sunbird or Kontact) or my phone (thanks to MyPhoneExplorer, which syncs with Rainlendar).
One reason for this, is that Rainlendar is careful with my calendar files. I fear that too much focus on syncing with Outlook (and to a lesser extent Google Calendar) may mean adding certain app-specific stuff that could ruin that. And even if it didn't, I suppose there is a price to pay in terms of code-complication (I may be very wrong).
Therefore I would strongly suggest that Rainy kept his focus on being truthful to the iCal standard in its simplest interpretation. That policy will, I hope, lead to best syncing features long term.
For instance, taking a pragmatic approach, a slight tweak to the RRULE element would increase compatibility with Kontact enormously. Still simple, still within iCal specs - but great user value (for KDE users, at least).
So, my reply to the question of focus of full sync implementation, would be:
Slight change to RRULE element and get Kontact compatibility. My bet is that it is by far the easiest of the three (Outlook vs Google vs Kontact).
Anyway - thanks Rainy for making the coolest calendar app I've seen so far.
More on the RRULE buisiness here: