I bought a nice pair of pants to wear to work, and I am reasonably certain they were of good quality (although maybe I was mistaken) and I found that the seat of the pants was worn down to holes in less than a year of near-daily commuting. I commute by bike to my workplace and I don't bother changing because it's a leisurely 15 minute ride and I don't work up a sweat, even when wearing business-casual attire. I of course use the bike to go elsewhere but it is the same in that I don't "ride hard", so to speak.
One thing to note though is that the seat was leather but cracked so there were some sharp edges on the torn leather which may have contributed to the problem.
I'm just wondering if anybody else has had experience with pants becoming worn out in the seat due to only light riding, and with an undamaged seat, because it will make me more hesitant to wear work clothes on the bike in the future.