Q1: Where do the QuickCounters get their data from?
Q2: When I start couple of orchestrations they properly show up as "Started" and then "Completed". If I leave QC alone this number will drop to 0, why?

Art - quickcounters are based on Windows performance counters. If you are seeing started/completed numbers drop back to zero, it is likely because you have restarted the biztalk host where your orchestrations were running. Note that "Requests Executing" will decrement if the orchestration dehydrates (and increment when rehydrating.)

If you are looking for real-time metrics to support performance testing and troubleshooting, QuickCounters are an excellent choice. If you need a long term view of the data, you would need to sample the performance counters with MOM or a similar tool. At some point, your needs will be better met by BAM if archival of actual start/completion numbers is important (as opposed to getting snapshot views.)

Scott,
Thanks for your response, it's been very helpful. Business will decide exactly what they would like to see and we will try to implement the solution based on their needs. Right now I think they will be happy seeing how BT applications perform at any given moment. We now have QCs exposed via WS and AJAX'ed, works really nice.
Again, thanks for your help!