So basically, you've got until newyears to get one ordered.
CCLonline[2] and ebuyer.com[3] are offering the servers for £180, so £130 after cashback.
I've got one already at home and plan on ordering two more tomorrow. Surprisingly powerful boxes, can take upto 16gb DDR3 (ecc unbuffered), internal USB and proper hardware virtualisation.
[1] http://h41225.www4.hp.com/UK_focus/PA0074%20-%20HP%20Microse...
[2] http://www.cclonline.com/product/108949/704941-421/Branded-S...
[3] http://www.ebuyer.com/430446-hp-proliant-g7-n54l-2-2ghz-micr...
PS> "zfs in raid 2" -I believe you mean raidZ, the zfs equivalent of raid5. raidZ2 (zfs raid6) would only leave you with approx 6tb usable space rather than the 9 you're quoting. As the microserver has only 4 drivebays (well, 5 if you use the optical bay) you'd probably get better speeds and same real space by using the zfs equivalent of raid10 rather than raidz2.