Nobody can publically say what the LR3 release date is without there being legal repercussions, until Adobe makes their official announcement.
The hints would be:
1) The LR3 beta expires at the end of April.
2) Adobe has a press event scheduled near the end of March.
That suggests at worst it’ll be within 6 to 10 weeks.
And both LR3 and CS5′s ACR will use a new RAW engine and will likely need to be released together, or within a few weeks of each other, so even if it is CS5 that is announced in March LR3 can’t be too far away, either.
I think Adobe will let you upgrade Photoshop for free if you buy it after the new one is announced but before it is available. I dno’t know if LR has the policy or not, since it is a bit cheaper. If you can entertain yourself with the beta until you can purchase the released LR3 it’d be $100 cheaper, but perhaps you cannot wait that long.