did you installed the ipkg for usb printer (kmod-usb-printer)
whem my box is idle the top looks like this

Code:
Mem: 61644K used, 1284K free, 0K shrd, 25340K buff, 18396K cached
Load average: 0.00 0.00 0.00
  PID USER     STATUS   RSS  PPID %CPU %MEM COMMAND
16205 root     R        436 16202  1.1  0.6 top
16201 root     S        564   562  0.1  0.8 dropbear
  669 root     S       5712     1  0.0  9.0 SABnzbd.py
  738 root     S       5712   670  0.0  9.0 SABnzbd.py
  733 root     S       5712   670  0.0  9.0 SABnzbd.py
  737 root     S       5712   670  0.0  9.0 SABnzbd.py
  735 root     S       5712   670  0.0  9.0 SABnzbd.py
  734 root     S       5712   670  0.0  9.0 SABnzbd.py
  674 root     S       5712   670  0.0  9.0 SABnzbd.py
  684 root     S       5712   670  0.0  9.0 SABnzbd.py
  670 root     S       5712   669  0.0  9.0 SABnzbd.py
  671 root     S       5712   670  0.0  9.0 SABnzbd.py
  672 root     S       5712   670  0.0  9.0 SABnzbd.py
  673 root     S       5712   670  0.0  9.0 SABnzbd.py
  732 root     S       5712   670  0.0  9.0 SABnzbd.py
  742 root     S       5712   670  0.0  9.0 SABnzbd.py
  740 root     S       5712   670  0.0  9.0 SABnzbd.py
  675 root     S       5712   670  0.0  9.0 SABnzbd.py
  676 root     S       5712   670  0.0  9.0 SABnzbd.py
  743 root     S       5712   670  0.0  9.0 SABnzbd.py
  739 root     S       5712   670  0.0  9.0 SABnzbd.py
Code:
root@OpenWrt:~# uptime
 12:52:24 up 20:38, load average: 0.00, 0.00, 0.00