Turns out the Acer W510 was supported, it was the language issue (UK English when only US English is supported) so I changed my language and location setting on Monday and installed.
I'm glad it's only my secondary machine as it's been rather buggy and unreliable since the upgrade. The upgrade itself took ages too, about an hour to download (about the same time it took to download the ISO separately) and then at least another hour to install and set itself up before I could use it. I know Atom devices are slower than the average but jeez, this was arduous.
The updates tonight seem to have it working better now but I'll play with it more tomorrow and see what happens.
To be honest, as cool as the new start screen and snap modes are, I've yet to feel a huge benefit* to the upgrade (though as it's my secondary device I suppose that's to be expected.) as most apps don't actually support the new features yet (even the Microsoft apps have only vaguely been updated to support the new snap modes as the new versions won't be released until RTM in August).
*That's not to say there aren't any though, 8.1 has a _lot_ of good new features and once it RTMs and other apps start getting updated to use them we're in for a much better OS experience.
Also, when it comes time to update to RTM it'll mean having to re-install everything again (even the metro apps! Only some of my previously downloaded apps were kept during the upgrade, and they still needed to be re-downloaded. I had to go into the store to find Twitter, Skype, and a few others to re-download and install them) so unsure of it's merits as this so far seems more unstable than any of the Windows 8 betas (yes, even the very first developer preview was more stable than this!).
If you do upgrade, I would *seriously* recommend using Windows 7 File Recovery (just do a settings search from charms to find it) and creating a system image so you can restore your existing setup in case anything does go wrong or you just want to revert back. If the updates from today don't make the tablet more reliable over the next few days I'll be flashing my Windows 8 system image back on it this weekend.
I've decided not to even bother upgrading my main machine (Samsung Slate 7). Though I did dual boot it to take a look over the weekend. It was a much quicker and less painful process to do a clean install (1 hour download, then maybe 20 minutes to install and setup) though obviously that also means having to start from scratch and re-install EVERYTHING.
Choose wisely, but make sure you have a backup system image just in case! :)