> And if the migration script crashes halfway through... oh man.

Schema-issues and typing aside, I looked at MongoDB just long enough to find out there are no transactions, then ran away, quickly.

For a lot of tasks, I guess I would find MongoDB very useful, but lack of transactions is a complete deal breaker for me. Not having a real schema, referential integrity and all that makes them even more important, IMHO.

At work, I have had more than one quickly-hacked-together Perl script crash on me in the middle of a run. Having proper transactions has saved my butt repeatedly.

By contrast, with Postgres you'd have an explicit schema which all records obey, and even migrations can be done in transactions.