Updated 05/25/2010, 6:06PM CST: An anonymous tipster from inside Google let us know that this is actually a release candidate and not a test build. The distinction is important, because a release candidate may end up being the final release unless bugs are found that require attention.
Updated 05/25/2010, 4:50PM CST: Our contributor Nate Kimmey pointed me to this update by Google employee Ry Guy on the Nexus One support forums:

Hi all,

Thanks for the responses!

Just wanted to give a heads up that the build floating around is not the official Froyo release. You will get an automatic notification when we OTA the build, no need to manually download it. You will still get the automatic notification if the official release is a newer version than the one you have, so don't sweat...but I'd highly recommend waiting for our official release :)

@Bhushan4181: You will get the OTA update as long as you are connected to the internet and can communicate with Google servers.

We are striving hard to OTA the build to you ASAP, thanks for your patience!

Gaurav.

This is as official a confirmation as we’ll get that this is not the final build of Froyo. Hopefully we’ll start seeing that roll out soon, but until then, run the build at your own risk (it’s been fine on my Nexus One)

Shortly after TechCrunch first reported that they received the Froyo OTA, many blogs, including ours, briefly speculated that the update was only being rolled out to phones that had previously been provided to the press for review purposes.

This is theoretically possible, as it’s likely that Google has a list of IMEI (International Mobile Equipment Identity) numbers that could be used in order to release a targeted OTA update.

However, TechCrunch updated their story to report that Google has in fact confirmed the OTA and once the file leaked, people didn’t seem to care anyways as they were just happy to have Froyo working on there on their phone.

That’s what makes this tweet from Android engineer Romain Guy so interesting:

2010-05-24 19h50_22

Since Twitter doesn’t provide the absolute time on their timestamps, this tweet was made at around 5:50PM CST on Monday, May 24th 2010.

So basically, if this is true, it means that the Froyo build that’s floating around out there is for testing purposes only. This may be the reason that Google killed the download link that had previously leaked.

I replied to Romain asking for details as to what may be different in the new build versus the leaked build, but he hasn’t responded yet. Hopefully we’ll be able to get our hands on the newer OTA shortly so we can see exactly may be different, if anything. At this point, I don’t think we can expect any drastic changes, but hopefully we’ll see a few fixes to some of the bugs people have been complaining about.

We’ll keep you updated as this progresses.

Source: Romain Guy’s Twitter