There is always a rule that seems to get pushed, prodded, pulled and abused in its proper fashion in a game. Some rule that is necessary to the game creates a whole slew of issues which frustrates gamers.
For me this is deep striking, and to a lesser extent blast templates in general (which I do love btw). Mainly this is due to the issues that arise from scattering, and with deep striking, the mishap table. No one wants to lose a good chunk of their army to the warp because of a half, or even a quarter of an inch difference in placement and angle of the scatter, or going from 3 wounds from your blast template to none.
