The worst-kept secret in Microsoft’s history may well lead to a surprise anyway. This afternoon, the company made available a program that prompts curious Windows users to download the latest Windows 8 Release Preview – the final preview before general release expected later this year. But Windows 7 users who run this little jewel will be surprised to find that it tries to upgrade their Windows 7 to the Windows 8 Release Preview.

The Windows 8 Upgrade Assistant, available here, assesses whether your existing operating system can be upgraded to run the new Windows 8 preview. ReadWriteWeb is testing the Upgrade Assistant’s efficacy on a partition containing the previous Windows 8 Customer Preview (the second of three). We have encountered no problems so far.

So, for now, we can advise you to run the Upgrade Assistant on (or more accurately, from) a partition containing a test version of an operating system, which may be either a disposable test copy of Windows 7 or an earlier Windows 8 preview. The program checks existing applications for their relative compatibility with the upgraded system, but even though we had installed multiple test applications in the Consumer Preview, the Upgrade Assistant did not offer an installation option that would let us keep any of them. “Keep nothing” was the only choice provided.

A Microsoft spokesperson told ReadWriteWeb to expect some of the improvements that many of us have been actively campaigning for. Once we see evidence of them, we’ll photograph them and tell you more about them here. One that we’re particularly keen to see is described as “increased personalization options for the Start screen.” Although tablet users testing the Consumer Preview have been impressed with the Windows 8 Start Screen functionality, the way in which it was visually segregated from the Desktop environment, coupled with Microsoft’s decision to make switching between the Start Screen and the Desktop more obscure, has been the principal complaint among Windows veterans (including myself).

One critical discovery: The “Keep nothing” choice, which may be your only one, means that whatever was in the “My Documents” folder on your old operating system’s home partition will be completely deleted. So make certain you back up any contents from that folder that you wish to keep.

More information, including screenshots, still to come.