Compared to GTA:SA, which felt like the territory attacks happened every ten minutes, it's much better. It was something along the lines of after every other mission there was a territory attack. However, I DID generally play through the story missions without really screwing around...I suppose there's a chance that it's actually a time-based thing rather than event based.
Still, I didn't feel like I would gain a territory and then five minutes later have to retake another.