A quick note on this excellent method of tracking one's progress through the unpainted pile:
1 28mm Inf figure = 1 OPP.
1 28mm Cav figure = 2 OPPs.
1 artillery piece = 3 OPPs.
1 small vehicle = 5 OPPs.
1 big vehicle = 10 OPPs.
On that basis my current total stands at 3 OPPs - Tau NCO, Varingr JNCO and Mordheim elf with bloody great big sword.
Ideally I'm aiming to get 8-10 OPPs a month, for an annual total of (roughly) 100-120 OPPs a year. That's assuming I only paint at work and in my lunchtimes...