The micro instance seems to be routinely throttled, for random reasons. My vm was choked for days despite only pulling in ~200 visitors per day. Upgrading to the Small instance has removed all throttling.

I'm running a standard LAMP stack on it, nothing crazy.

hmmm, yeah I have noticed weird behavior a few times, however I run a Java Spring app on there and most of the time it works, its pretty much me that is using it though, I would think that Ruby does use more memory than Java though.