SP AI definitely still questionable.

[Archonsod]

Gandalf Parker said:
The problem seems to be that if most of ArmyA is wiped out in the first couple of provinces, its still ArmyA. And that army gets sent out over and over until its gone.

Its the disband or refill code that seems to be lacking. Im not sure how often it checks its armies trength or rebuilds them.

I'm not so sure it's a problem. I've noticed the AI tends to move several armies into a position to attack the same province. While the small army attack isn't going to win, it can put you in trouble if you can't replace the troops it killed before the larger armies attack.
I've seen the AI use attrition type tactics against my better defended provinces a few times. I was quite impressed actually - the province it was attacking was essential to my supply lines to the South, and it repeatedly hit it over four turns. I had no castle nearby, so it ended up grinding down my numbers before launching a huge army into the province, well before relief could arrive.