I suppose at this point we're all piling on what seems like a bad business idea. My main complaint from the user side is that at $15 a month for a small set, you'd have to turn this around at least a couple of times a month to make it worth while. Otherwise, why not just buy a small set each month, and you wouldn't have to worry about finding all of the pieces and boxing them up, taking them to the post office, etc. I just don't see the turnaround being efficient enough to merit this. BTW, that's part of why we stopped getting the discs-through-the-mail option from Netflix when they changed their pricing schedule. If we would get a disc, watch it that night, send it in the mail the next day, and few days later get another and repeat the process it would be worth it, but we just don't have the time to watch that many movies. The streaming option, otoh, is great, as we can watch whatever on the fly. Until they invent a transporter, that won't be an option with LEGO.
On the business side of this, I'm shocked that they have a 'no charge for missing pieces' rule. That's just begging for essentially all of the figs to go walking. I don't see AFOLs using this as an illicit way to get some rare elements, but I do see kids just playing with the figs all over the house (I'm always finding figs in the edges around my son's bed, for instance, as he often takes a couple to sleep with him), and the parents not getting everything back in the box.
I do see one potential plus to signing up for this system. If you signed up as a 'mega fan' for a limited time, you could get a chance to put together some of the bigger sets that you may not ever purchase. For instance, they actually have the Death Star, 10188. I may be a castler, but Star Wars still runs in my blood (I was eight when ANH came out, the perfect age for it to be a life-defining experience). I'm never going to plunk down the $400 for that set, but I would really love the chance to build that set just once, and spend some hours reenacting all of the key scenes from the movie. If I didn't have kids* I might just sign up for this service for a couple of months, just for the chance to run through and try out some of the really big sets I'll never buy. I see they also have the Super Star Destroyer and a couple of the Cafe Corner sets, other things I'd love to build once or twice but would not purchase.
Blue, you almost gave me a heart attack with that superglue revelation. I do think someone should call child protective services.
*Don't get me wrong, 98% of my LEGO building, and the most fun part, is with my kids, but their "help" makes assembling large scale models in the middle of the living room pretty much impossible. My personal building is generally reserved for after bedtime, and on my workbench in the garage. That probably also explains why I post so few MOCs.