I basically agree with what dionysus stated in the first post:
A Bonus should never be imposed automatically, unless maybe it's Free Spins for a deposit, that have NO impact on the balance, i.e you can play them later, but generally i think a pop up and/or check box is the responsible and player friendly way
I also think that the few Casino's still out there that do impose a Bonus on the first or whatever deposit, should at least have the decency to inform their players with a pop up too, something like "click here to agree to the T&C that are attached to the Bonus you will automatically receive on your deposit"...but i guess that's a far stretch.
In contrast, i must admit that if i DO tick a checkbox or use a code to receive a Bonus, and that then doesn't work, i am generally disappointed, to say the least
In most of my regular Casino;s this would not present a real issue, as there it's often quickly fixed by support, but imagine your average joe Casino, but admittedly also a few where i play, that don't offer the stated 24/7 support, which could turn a prospect of a fun nightly session, into a long waiting game instead.