Saddles and Bent Metal Rails
I have not just had them bend I have had them fracture. 
I took my saddle to the shop thinking they would say "wow how did that happen" and the response I got was it happens all the time - that saddle is a few years old. 
Aluminum will fatigue - low end seats have a limited life. 
A steel or titanium seat does not suffer from fatigue (will not at nearly the level of aluminum). 
Carbon also is reported not to fatigue but I don't have any experience with carbon railed saddles. 
Inspect your rails on a regular basis for deformation or cracks. 
If you go out the back and land your bumm on the wheel because the rail fractured it gets a lot easier to spend $100 on a saddle.

I think the seat position was also a factor as I had the seat all the way back.  What that does is create a longer lever from the back of seat to where the rail is clamped.  I also put an offset seat post on the bike so I got what I consider a better clamp position.