You need to make sure you have lots of screen shots of completing the offers and will probably have to chase Ladbrokes up for them to pay out on the offer.

I think it was Ladbrokes that I did the offer with a few years ago and it took a screenshot of the welcome email, a screenshot of my deposit and of my bet (I think you have to make a bet too to activate the offer) and about 3 weeks for the offer to come through.

If like me you bet a lot, its worth doing, but if you are just joining to get the offer I would say avoid.