QR is alright for the rear, upfront you definitely want to go 20mm, if not solid axle 9mm..
I love my 20mm axle, however i have a QR on my rear, and I love that too. YET to see any forms of problems with it and ive had it for 2 years. How is force put on the axle though ? It would have to be really brittle to snap woudlnt it, considering its your hub which sits in the drop outs and the QR clamps from either side.
I think a strong hub can help with it, I've never heard of breaking quick releases, only bending the hell out of them. I run a 440 in the rear and it seems to be doing just as good as my solid axle was. Taking it off/making adjustments on the fly is much easier as well. Running a solid quick release also helps, I prefer the steel shimanos versus a lot of flimsy aluminum models.