here a quote from Sensei`s Library:
There are some situations where Gnugo just screws up EVERY time. If You know them, Youll improve Your performance against Gnugo considerably. Dont let this fool You into thinking You got stronger: Gnugo just never learns (unless its a version update). By adapting my playstile to Gnugo, I can improve my results in games against Gnugo by about 100 Points, compared to normal playstyle.
READ MORE HERE!
Another interesting point when we talking about computer GO comes from Shimari:
"I have been playing against SmartGo Pro on the iPhone, which does not use the GNU Go engine, but is considered reasonably strong on 9x9 and 13x13 - maybe 5 kyu. I agree with your point that computer play is great for basic tactical training and it will ruthlessly punish mistakes.
It does not really have a strategy though, which is one reason why its play gets worse on the bigger boards. Also, once it senses it is losing, it starts to play strange moves, such as placing a stone where it can be captured. Presumably the reasoning is that you might overlook the capture, in which case the computer would be ahead. Humans generally don't do this!
I noticed the same thing with a chess computer I used to have. Once it was seriously behind, it played completely crazy moves, probably reasoning that any move left it as badly off as any other."
You should give GnuGo a try Shimari ... it is about ~8kyu (perhaps 5 - 12 kyu :-D ) on 19x19! And it is free!