I realize you targeted another Thwackster, but thought you might like knowing my organization uses screen sharing very frequently. I use it about a dozen times any given day during meetings. It works perfectly for me internally. Getting it going between our internal clients and other businesses' clients across the Internet sometimes is a little flaky, but MS and our VAR have been helpful getting the kinks worked out. Often the issue is new ports or poorly-documented functionality requirements, resulting in changes needing to be made to our servers or firewalls.
We've not found anything we haven't been able to work out yet, but it took years to get to this state. I REALLY don't like the Internet/DMZ/Internal server/firewall rules required for the resilience and functionality we need. They are the most complex solutions I've ever implemented, and it's hard not to think they weren't kluged together without a great plan and top-notch design overview for efficiency.
Here's praying that Team will be easier to deploy and more reliable.