I have had a number of Smiths over the years and I have never managed to damage one. I think the frame stretching issues were problems with aluminum framed guns and were limited to people who routinely fired high pressure loads. Cracked forcing cones? Yeah, fire about 10,000 rounds of full power .357 through it and you MIGHT crack it.
As far as reliability goes, I did hear something a long time ago about the 686s locking up under full pressure rounds. Don't know what the cause was, but haven't heard anything else after that. I've never heard anything bad about the 66 (or the 19, for that matter), other than that you shouldn't run a high number of full power .357s through them.
BTW, my favorite revolver is a Smith 66 2 1/2 round butt.