I, along with probably half the known world, got the "Reserve your Windows 10 upgrade" task bar icon last night.
I've done the reservation, and so now I have until at least the 29th July*3 to work out if or when I go through with the upgrade. I've typically been a slow adopter to new versions of Windows (still feeling pretty smug about dodging Vista!). I generally agree with the new direction of Windows...incremental updates makes far more sense than big-bang every 2-3 years, and getting rid of the massive variety of OS versions out there can only make developers lives easier*4. I've been running with auto-updates ever since I made the step away from desktops to laptops.
I have a fairly decent spec laptop, so don't really have to worry too much about the minimum specs, and most of the "depreciations" don't impact me (I don't have a DVD Drive, use Media Centre, or use the built-in games. Can't remember the last time I even saw a 3.5" floppy disc!)
I'm currently on Windows 8 64-Bit, and getting on OK*1 with it. I'd had a bit of experience with other machines on Windows 8, so knew how to get rid of all the shite tile-based navigation pretty quickly. I think my main worries about upgrading are;
1) Drivers - while I have a pre-built machine, it's not got the most common hardware (26 similar system tests in 3DMark for Sky Diver), so there is a risk that once I upgrade, I'll find some hardware doesn't play nicely.
2) Loss of installs - games I'm a bit less worried about, as pretty much all of them are on my Steam account, so can be re-downloaded (a PITA, but nothing else). I have a fairly old version of Office (2007) on the machine, which I got as part of the Microsoft Home License scheme, which my company doesn't support any more (fortunately I kept the install files and the key when I originally bought it a few years ago)
3) Horrific Bugs / Design choices - this is what has kept we away from new OS'es for a couple of iterations previously...while on the face of it most of the design choices seem to make sense (Start button is back), there is a reasonable chance that there will be some sort of fairly serious issue on day 1, simply due to the large variety of hardware that needs to be supported (and as mentioned above, I don't have the most common hardware, gaming laptops being somewhat of a niche market).
My gut feeling is that I should probably sit on my hands for a couple of months, and let other, braver early adopters take the initial hit in terms of pain...
*1 You'd struggle to tell, as I've installed Classic Shell and Fences to sort out navigation.
*3 as I understand it, you have a year once Windows 10 is released to do the free upgrade...after that time it may be charged, though of course this may well become a moving goal-post.