So, I've been watching top for awhile thru ssh and the snapshot below is about as busy as it gets (only showing 4 "busiest" tasks).  Didn't see any change in free mem past 30 minutes.

top - 21:06:23 up 1 day, 17 min,  2 users,  load average: 0.38, 0.36, 0.40
Tasks:  70 total,   1 running,  69 sleeping,   0 stopped,   0 zombie
%Cpu(s): 11.7 us, 14.9 sy,  0.7 ni, 71.5 id,  0.0 wa,  0.0 hi,  1.1 si,  0.0 st
KiB Mem:    448736 total,   248020 used,   200716 free,    44180 buffers
KiB Swap:   102396 total,        0 used,   102396 free,   157248 cached

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND
10617 root      20   0  243m 4820 2704 S  22.1  1.1  14:40.26 cgminer
 2213 root      20   0 24452 7464 2340 S   2.3  1.7  20:40.24 wicd
 2249 root      20   0 14980 8048 3996 S   1.3  1.8   9:13.03 wicd-monitor
16550 pi        20   0  4808 1620 1032 R   1.3  0.4   0:03.76 top


Edit:  Couple hours watching top and cpu loading is the same, though I do see a slight decrease in free memory (about 700KB) -- a little exploration showed it matches increases in the various log files, but this tells me running out of memory is probably not the cause of the random sem_post problem.