Finally ran my first Shroud run last night, and I have to say that it went very smoothly. There was DPS galore, many twf-er's, many firewalls and bb's, etc., etc. There was the occasional hitch but overall I didn't encounter much lag at all. A tiny bit of rubber-banding as the group ran from portal to portal, but no real network lag hardly at all during the Harry fights. This was in prime time.
I noticed in the VoD run I participated in right after that more pronounced lag, but hardly annoying. One member of the group commented that his system chugged down to like 3 fps during the Sul fight near its end, but my system was humming along without any noticeable problems. I was actually surprised since it was complete chaos, especially when the bats hit. Running through the Subterrane I do notice some stuttering, but I believe that's related to the textures and geometry of that area as opposed to any severe lag.
In the end I believe (so far) that if your system is running DDO at a nice steady clip of 40-50 fps or more for example when in the marketplace, AND you have a decent ping time with a nice solid connection, things should be fairly smooth. I may change my mind on future Shroud runs, however, but I guess I lucked out last night.
Oh yeah, I pulled a large scale, as well.