I think I'm gonna wait it out a bit..
I'm going to check some time after deliveries started if one little single from butterfly labs can still produce enough btc to recoup the investment in max 2 months.
I want at the very least 1 btc a day.

Once deliveries start, maybe somebody will be able to post what he is earning with his little single at that time.
This would give me a real valuable indication whether or not to buy.

I also think that once deliveries have started, butterfly labs will be more able to provide a correct delivery date.
I'm not that afraid that the equipment will become unsellable (unless bitcoin dies of course)
But it would be rather stupid of me to buy something and almost immediately sell it with a loss (given that I can estimate my profits)