Obviously you will support PHP 5.3 but I just wanted to get some official feedback that you will be officially supporting the newest revision (to be released in the near future -- before IPB 3.0 Final.

I'd imagine it'll be tested, but as PHP 5.3 is likely to be released after IPB 3.0 anyway, I wouldn't expect cast-iron guarantees it's going to be 100% compatible - there may be small bugs/tweaks to be looked at after final.

Obviously I can't speak for IPS, but I'd be surprised if they said anything different.

I don't think anything in PHP 5.3 is going to break IPB. That said, the latest version I've tested with locally is 5.2.9.