PIAA, the reason I suggest "arms up" (and I'm talking arms and hands, here, not elbows or shoulders) is that I think it's the best way to fend off the obstructing fielder. If you don't push him out of the way with your arms, the contact will be more, not less, serious. The problem would be avoided if umpires were more aggressive about calling obstruction in non-contact situations, but that's a tough call, which most umpires (at the levels we're talking about here) don't often make. I've seen a lot of runners detour around a fielder with no call (and given the skill level of the players, I'm not suggesting that that's a bad thing.)
In the real world, I think baserunners at the HS (and below) level have few options: avoid contact (and get tagged out, because you won't get the obstruction call just because you hesitated or swerved off line), or make contact (and probably get the call.) I want my guys to make contact. Safely, and obviously. That means hands up, to me.
While I regret the hissing match which erupted over this question, I think it's a legitimate one. So, what do you feel comes under the category of "all possible short of 'arms up and shove'"? I'm having a hard time visualizing contact "short of" pushing off with the hands.