For the part regarding database migrations, you can find here [1] an interesting podcast about SQL database (schema) evolution. Among the other things they talk about how to have multiple schema revision coexisting at the same time. While hopefully most of us just need to support at most two revisions at the same time, it gives a number of interesting ideas.

[1] http://www.se-radio.net/2012/06/episode-186-martin-fowler-an...