If I recall correctly (and a simplistic search of Google seems to support this), Parhelia did indeed also support (2 x 1) + 1 setup.Eyefinity does add a bit more to it than just 3 displayed and a single virtual display.
For the current shipping cards it also adds 2x1, 1 monitor configurations. Where you can have 1 virtual display of 2 monitors and another display.
Now of course, I very much doubt the supported aggregating the displays across multiple display devices, and it doesn't look like they supported rotation of the displays. I also found the resolution limit, no single display could be above 1280x1024. I don't know if that was a DX issue, or just a technological issue, or a driver issue, or who knows what.
I think this puts Eyefinity back in the evolutionary stack rather than revolutionary. Not that it's a bad feature at all, I'm glad to see it back honestly. I'm also excited to have the option to have my dual displays get the full start menu across both devices in Windows without having to go get secondary software.