There is no "collateral" anymore. You will be charged 0.1 "randomly" while you are using Darksend. This is to prevent DOS and other Sybil like attacks from occurring for free.
The charge should be rare according to Evan in the first post, so it looks like you had a run of bad luck.
Of course it could be a bug...
good to know
i was wondering what was going on as well
but most were zero payments or tiny amounts.
tiny amounts are still traceable though ?!