It happens on regular accounts, not just Business, I've seen it this morning when I got messages intended for somebody else.
I would refrain to send any sensitive information over Google Talk right now.
Why only "right now"? Why ever send sensitive information over a 3rd party's server. While I believe that Google will find and fix the problem, they probably make little to no claims about the level of security they offer. So using them at all should be a calculated risk.
What you shouldn't do is transmitting sensitive information without controlling the end-to-end encryption chain. If you do that, you can involve as many third party servers as is convenient.
Actually, this is what I meant and I should have been clearer. Thanks for pointing it out.