I've always been curious to know how much rain pants cost on a per-trip used. If for example the pants cost $100, but only get used 50 times before being discarded/lost/stolen, well that's $2 per use. Not a great deal. If, however, the pants cost $50 and get used 200 times, that's $0.25 per use, which is much more reasonable. I'm finding that even in the Pacific NW rain pants are not a necessity on most days. Oftentimes the rain comes and goes and thus on some "rainy" days, even days with a 100% chance of rain, it may not be raining during my commute. I doubt I'll be using my rain pants more than 40 times in a given year. Possibly as few as 20 times/year. So here are my questions:

1. How many years did you get out of your last pair of rain pants?

2. What caused you to replace them?

I never really looked at it that way. I've got a couple of pair of cycling specific ones, along with cycling specific rain jackets, and then a couple of pair of general rain suits, Frogg Toggs brand. To date I have only replaced one pair of the Frogg Togg bottoms, which run around $30, victims of a vicious dog mauling which completely shredded them (ok, so it was my black lab when he was about 7 months old, got the closet door open and had fun chewing them up while I was outside washing my car.

I bought a good pair of goretex rain pants for commuting and quickly got rid of them. Honestly, wearing a good pair of wicking shorts and good shoes is the best, as your legs are naturally waterproof, better than goretex. When I get to my destination, I switch to dry and warm pants kept in my commuter bag while the quick dry shorts dry.
So for me, I spent 150$ on these pants, and wore them twice, and now they are my ski pants and camping pants.. nothing more.

I rarely use my rain pants. I save them exclusively for touring. I don't mind getting wet legs. I'll wear shoe covers and I'll wear waterproof jackets, but if I'm just commuting and not riding for 12 hours a day on tour, wet legs are fine with me. I just wear normal cycling shorts or pants, and let them dry while I work.

I use them.
I normally buy them as cheap as I can get them.
Their demise is the chain chewing up the right leg.

My next pair will have velcro straps to keep the leg out of the chain.

I just wear leg warmers or tights in the winter. They dry out by the time I have to go home. If I wore rain pants my regular pants would get wet.

My attitude is that the rain gear is just part of my bike, like fenders, that make it useful for riding in all weather. My last set that wore out, simply became porous over time. I got a couple more years out of each piece using a waterproofing spray from REI. Now the rubbery inner layer of the rain pants has worn through in the crotch area. I commute in my street clothes, and don't sweat a lot, so a rain jacket and pants works pretty well for me. I also use the same gear for hiking, or if I have to be working outdoors for some reason.

I suspect that the materials undergo some sort of chemical deterioration, so they would last the same amount of time no matter what.

One suggestion: If you regularly carry rain gear, put it in some sort of bag to keep sunlight off it. Most synthetic materials deteriorate under UV exposure, including directly from the UV, and from the ozone generated by UV.

Don't really know how long they last yet..........my four old Showers Pass pants left me looking like I peed my pants when I got to work last week. I don't care at all. There is NOWHERE to change. I was wearing Woolies underwear so it didn't bother me a bit. They just went through the washing machine with Nikwax Tech Wash and TX Direct Wash-in.

I guess I'll find out this Wednesday/Thursday.

I bought a pair of O2 Rainwear pants (the black ones) back in 2007 for $65. I still have them and use them when necessary. They are always in my bag. Excellent rain pant. Good breathe ability and excellent in a downpour. They are not insulated but I have worn them several times in a freezing rain.