I've actually watched a bunch of Poker Training videos on rebuy MTTs and prior to watching my first one a couple years ago, I always thought a rebuy was basically a donkfest (I had no clue).
There's actually alot more going on than what appears to be madness (there's a means to the madness). Typically in rebuys you don't get moved in the first hour (unless you have a bunch of 1-bullet players (folks playing them like a freezeout) so even if you donk off your stack, the chips are staying on the table so when you rebuy there is now more chips for the taking on your table (in other words >> you've lost them.. BUT they're not completely gone).
A rebuy tournament is basically a deepstack tournament that starts once the rebuy period is over. One needs to have a decent stack if they hope to be competitive after the rebuy period (or if they hope to have a playable stack with an M of '20'+).
I've watched a few rebuy MTT videos on poker training sites and have learned alot about the strategy involved in them. They're actually pretty decent tourneys and favour those who are familiar with playing deepstacked poker, whereas most of the tournaments online are pretty fast-structured games (ie. the 1500chip tourneys don't leave much room for gettng involved in more than a couple of hands in early levels.... not much forgiveness there and only have implied odds to set-mine & play SC's in the first couple of levels, the double stack tournaments are a bit better (but once the antes kick in the avg. stack is nothing more than a re-steal-size stack so in many instances, if you're open-raising you'll often be wanting to do so with a hand strong enough to be able to get involved with any shorter stacks who might be playing back at ya).
There's one documented case of a rebuy tournament that Daniel Negreanu played where he rebought an insane amount of times (I forget how many times... I'll look it up).
Brad Booth - > "Like a fight... it's not how you start, it's how you finish"