We're almost there! This is the home stretch, people! After months of technical previews and feature introductions, Windows 10 will finally be upon us tomorrow and you'll be able to enjoy the glories of having a Start Menu again. Some of us will, anyway, because not everyone is getting the free upgrade on July 29, since Microsoft is planning to roll the new OS out in waves. The weird thing is you might already have Windows 10 hiding on your machine.
When you went through the process to "reserve" your digital copy of Windows 10, you agreed to allow Microsoft to download the necessary installation files for you whenever they became available. This involves gigs and gigs of data, so the download can take a while depending on your connection speed. Possibly in an effort to mitigate this issue, Microsoft has apparently already started pushing out the installation files to people on the list, except the files are being "hidden" and staying dormant until the folks in Redmond give the green light.
If you hop on over to C:$windows.~BT, you might find that you have some new files hanging around that weren't there before. That's apparently Windows 10, downloaded automatically just like how the software updates are going to be downloaded automatically for the next ten years.
If you have the files in that directory, then there's a good chance you'll be greeted with a "Welcome to Windows 10" kind of message tomorrow (it's actually right at midnight EST tonight if you want to stay up to find out). If the files aren't there, that probably means you're not a part of this first wave.