Quick update:

• With snappy, my last rebuild took 4.5 hours after deleting the .armory/databases directory.  There's a lot of room for improvement on that one, but a lot of the options are kind of heavy changes, and it's not critical for stability.  I'll try now it without snappy and see if it improves.
• Displayed balances are really incorrect when used on mainnet.  Perhaps it has to do with length of history.  But luckily, it's an "aesthetic" error -- I just confirmed that the raw DB entries are 100% correct, the interface is just reading the DB incorrectly.
• You can expect a whole bunch of errors and warnings when you restart, because my code accidentally rescans the last few blocks and then triggers those log entries because things that it's expecting to be unspent are already marked spent, etc.

And most importantly:

• Armory uses 288 MB of RAM after the DB build is complete (on Linux).  That's means that Armory online mode should be usable on even a lot of older hardware!
• There's a compile-time configurable parameter to adjust how much RAM is used when it's building the DB.  Right now, it's set so that it won't use more than 1 GB of RAM while building.   I will make that run-time configurable and do some testing on it RAM-vs-performance.