Mirroring all of the information that bitcoin keeps about transactions inside your bitcoin-oriented web app is probably not the right way to go.
It violates the zero/one/infinity principle, and you're likely to have subtle bugs if (when?) the two copies get out of sync.
See: http://www.bitcoin.org/wiki/doku.php?id=accounts for "best practices". If you're willing to share what kind of thing your web app is doing, I'd be happy to brainstorm other approches, too...