Nice simple question - what is your preferred points limit, and why?
For me, I like the 2,600 point mark. Whilst it prevents Grand Armies, you're usually able to get the toys out, with a few critical choices to be made. Characters wise it opens up all non-special characters, as well as the vast majority of mounts, whilst keeping such things a compromise.
In addition, the armies can typically sit on a 6'4" board without packing it out, allowing room for manouevre (well, unless your really really fond of cheapo troops!)
Somehow, it just feels right for a pick up game. Plus the army can quite easily be deconstructed down, and your just a couple of units short of a Grand Army for really big games!