We have 2 boxes with this Supermicro board and PFsense 2.0.1 running. One Year it was no problems at all, no restarts, very stable. Since today morning we have the same problem with these two boxes. Suddenly reboots, weird hdd problems (says it's full but it isn't full and fsck and smart and vendor tools say it's all right with hdds). ram is OK. CPU temp on one box 38 and another box 21 Celsius. It's looks like something with cable or sata controller. It's runs with one hdd, no raid.
For 3 month I had the same issue with another boxes (absolut the same hardware configs) at my customers Datacenter. All was running about 6 month good and suddenly both boxes weird problems, reboots and so on. Those problem was solved changing sata cables and hdds from WD black scorpio 160 GB 2,5" to Seagate. Now they running 4 Month with no problems.
And today these problems in our Infrastrucure too :( There was IPMI update at supermicro website -> now installed and waiting if it helps. box #2 since 5 hours -> OK, box #1 since 1 hour updated -> no crashes.
I'll keep You updated if anything goes wrong, but for me now: no more these Boards with pfsense.