Thankfully I have never had a frame failure personally although I have seen plenty through abuse and total misuse, (or accident).
I have to agree with the Saracen comment though, the early Saracens, Trekers and such like with double U brakes, Wow, not only were they substantial in there frame fabrications, I don't think I have ever taken any other British assembled bike out of a box and had it any better assembled than those early 90s Saracens. Exceptional.
My Early TBG Explosif seems to have taken a hell of a punishment and yet no a murmur of a problem in the last 24 years.
Bontragers, well they just do what they say on the tin, and never give up. Supple Forgiving and yet Strong in its makeup.
Roberts D.O.G.S B.O.L.O.X...., far more expensive and detailed in its make up, perhaps tipping the scales in terms of ride feel, weight and quality, and as you would expect from a Bespoke bike, Flawless. Even the Original Paint is bombproof. But then of its time it was spoken of being the Ultimate in steel, I guess the original Bike magazine testers original views have been born out from members here after 20years of use.