a) Unnecessary hits to the database. Due to the fact that files can reside under /packages/acs-subsite/www and be mounted under that package, we always hit the database unless we would announce for the / that we loaded all children. Which excactly is not the purpose of lazy caching. So the occasional hit to the DB is in there. Same is true for directories under /www.
To solve this issue I have come up with a list of reserved names under / which will not trigger a trip to the database. At the moment these are the usual suspects "resources images image x o file admin". As this is a list of names you are not allowed to use when mounting a package, maybe we can get this list complete and also make sure that noone comes with the idea of mounting a package with that name in the first place?
b) Much more testing needed. I have it now on a busy production site, but this is using acs-subsite a lot and does not make use of dotlrn. So maybe someone with a busy .LRN site could test it again? Also I'm not sure if all the issues reported by Gustaf have been fixed.