Thanks for the feedback.
To be clear: the only purpose of releasing a LR version 2.7 at all (RC or not) is for new camera support. In other words, the only reason is to support LR customers who have one of the new cameras (e.g., Rebel T2i, Panasonic G2, Sony A450, etc.). It follows that if you don't have one of these new cameras, the release won't interest you. And as expected, all of the feedback provided in this thread so far comes from users who do not have one of the new cameras. That's ok.
As for the reasons for the public RC: I also want to be clear about this. I strongly object to the suggestion that Adobe is getting lazy and simply wants the public to beta test their upcoming releases for free. There is a ton of internal work that goes on, under many different machine configurations and system environments, to get the best coverage we can for all the new models. So we feel reasonably confident when we put a public RC out there that it's already in pretty good shape (perhaps even final shape).
So why do a public RC at all, then? For these reasons:
1. We often add camera support by working with early sample files provided by the camera makers, or by working with early preproduction (with early firmware) units loaned to us by camera makers. Overall, this is a good thing for our users, because it means we can get camera support in much earlier, compared to if we waited for the model to ship publicly. However ... sometimes there are bugs & glitches in the files/hardware we have. Raw processing methods that are optimal for these "early" images may be suboptimal for images captured by final camera hardware/firmware (i.e., the ones that customers actually have in their hands). So the public RC is one way to help find out these unexpected changes and fix them before final release. (Yes, I know what you're thinking: If something changes between early and final hardware/firmware, wouldn't it be better & easier to just get an update from the camera maker directly? Agreed, but it doesn't work that way.)
2. As thorough as we try to be internally with our test systems, our users have more system configurations than we have. All different combinations of processors, memory, disks, OS versions, etc. We strive for as much coverage as we can, but collectively users invariably have more. So occasionally an obscure issue gets noticed this way during the RC period.
3. For the early adopters, it does give them a way to get almost-final support a few weeks earlier. If you've ever seen the threads in the Adobe user-to-user forum, you would know that early adopters are very insistent about having software support the very minute they lay hands on the camera! I recall getting berated a little over a year ago because a user had just picked up a D3X and had to wait a week before LR supported it.