1) database mirroring can be a WONDERFUL HA tool to put in place. But before ANY entity embarks on an HA implementation they need to REALLY spend some grey matter determining what they NEED and can PAY FOR. Then make a plan, implement, TEST, and monitor. In my 15+ years of SQL Server consulting almost NO entities have done that, from mom-and-pops all the way through Fortune 100 global companies.

2) Yes, checkpoints are done automatically. Look them up in Books Online (a MARVELOUS resource). They can also be done manually.