I believe this will become a common scenario, whether we are talking about Cisco or another PBX vendor, the ability to tie a phone system into a PC's user experience will become an important way that we enable employees to collaborate and become more effective in their communication.
As far as Cisco goes, you are correct that there isn't any need for a mediation server as the Cisco Presence Server essentially accomplishes this task of "translating" between SCCP and SIP. The benefit of using this scenario is the ability to put the phone routing, security, quality of the call, etc. in Cisco's hands and you need only use the MOC client to initiate calls -- less complicated OCS environent. So, if you have a fully functioning Cisco environment, you can leverage the investement and integrate with OCS and not have to worry about that layer of complexity.
1 - MOC can RCC any SCCP phone -- IP Communicator to CallManager is just another phone, so you can use MOC to conrol it.
2 - That's a good question, I need to try that scenario in my lab, but I believe that it will relate to how the phone is associated and how CUPS handles multiple line appearances -- more to come.
3 - RCC is a great way to give end-users "click to dial" which in a Cisco world can be a big leap forward. You do give up some of the tighter integration pieces like adding video to an established call and the ease of creating a conference call, but you can always fall back to the phone and do it from there.
Like I said I think this scenario is going to crop up more and more. It seems to me that end-users can really benefit when you combine some of the best from both worlds.
