Most of the time, in a tourney, I'd say check it down to try to eliminate the all-in.
If it's nowhere near the bubble, and the all-in has no chips to speak of (i.e., the pot is teeny), just play normally and ignore the all-in.
If on the bubble or at a crucial point (another level in the money), definitely check it down with as many people as will play. The only betting that should be done had better be with the absolute nuts. (Some will check it down with the nuts, too, but will play happily if someone tried to take a stab at the pot. Be warned.)
The point, right then, is to eliminate the all-in. Don't be a jerk and bet with nothing, leaving the all-in alive and well. The assumption that a bettor has the nuts, so most everyone else will fold and everyone is gonna see your stupid hand fail miserably.
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