If I add spock:0.6-SNAPSHOT plugin to my grails app, whenever I'm offline, running "grails" fails as it can't resolve the plugin. It's in my local Ivy cache of course (from previous times I ran grails when I was online) but the resolution logic seems to insist that SNAPSHOT items must come from t'Internet every time. Ideally it would fall back to the locally cached copy when offline.
Further to that, maybe performance in all situations can be improved by not going to the internet every time? Personally I would prefer it to never go the internet unless it didn't have a cached copy locally yet, or I ran an explicit update-snapshot-dependencies command to tell it to get the latest as a one-off. Having your dependencies potentially changing underneath you is a variable most people surely don't want whilst developing their own code.