Had a look at one today...
The possibility of being able to buy a magazine (or comic) appeals, rather than having boxes of magazines, or shelves of TPBs does appeal.
If Rebellion for example, released an iPad version of a TPB as well, or back issues of magazines I'd be interested.
The big question for me, is if a company did that, what happens if the publisher goes bust, you've then possibly lost access to everything you've bought.