I think they are pretty much a waste of time. You can spend 2-3 hours playing and then get knocked out by a bad beat before you reach the bubble. Call that fun? Even if you get a bit further you only end up taking away pennies.
I think they would be more interesting if they varied the type of game - how about an Omaha freeroll or Razz?
I was going to suggest a bounty element, but this would lead to even more all-in donking than there is at the moment and that is way toooooo much.
The idea from one of the posters above to multi-table freerolls from different sites at once is a good one. This might make the whole freeroll experience a little less tedious.