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).
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).