I'll be doing cartwheels once someone gets ZFS working on this, so I can plug in a bunch of USB hard drives through a USB hub and share a pool over the network.
(In the mean time, I have a Dell box doing this for me, though it was hard to set up. It took hours of debugging to figure out that OpenSolaris would crash until I disabled the second core/SMP. Then, it took hours to find out that the network crashed randomly due to a driver bug, and to find the right hotpatch off a random forum thread.)
I'm not sure how well you would get ZFS working on it with so little RAM, although it may work better on OpenSolaris.
On the other hand, I've got an Intel Atom processor, running with 1gb of RAM, and it runs ZFS reasonably well on FreeBSD. Mind you, this does have a much larger footprint, although it does have some advantages (mine has 3x sata ports built in, plus a pci and pcie port for more if I wanted, plus a dual core 1.6ghz processor). It was only marginally more expensive ($80 for the board/processor, $15 for the ram, spare PSU and case).
(In the mean time, I have a Dell box doing this for me, though it was hard to set up. It took hours of debugging to figure out that OpenSolaris would crash until I disabled the second core/SMP. Then, it took hours to find out that the network crashed randomly due to a driver bug, and to find the right hotpatch off a random forum thread.)