I wanted to write something technical about this issue to supplement a complaint I made a while back, and just found that someone did:
http://editthis.info/sonar/Sonar_Workflow_-_Multisesson_Tracking_Loopback_Latency
The date on this document is 2006, and I didn’t fully understand the problem until late 2007. I wish I’d seen it earlier!
Unlike the author though I haven’t seen loopback (or loop-back, whatever) latency since switching to ASIO drivers. I’ll keep testing for it then.
Here’s one for Audacity too:
http://manual.audacityteam.org/man/Latency_Test