If I get 10 years out of it, it'll cost me roughly £100 / year for reliable no worry usage. If I sell it for 80% of what I bought it for....then that's even better.
Same reason here for upgrading from the 100mm non-L macro to the L version ... and my primary concern with the new non-L IS lenses, it's seldom mentioned in tech geek threads. I don't buy red ring because it looks cool (actually I taped it), but because it's much more reliable, and even after less than 10years I'm pretty confident with my 100L/70-300L/17-40L.
You both make fair points; however the build of the new series of IS primes is a big improvement over the old 'consumer grade' lenses of the past. Time will tell how robust they really are.
Personally I use less L glass now because of the AF accuracy and adjustability of the new cameras, so I basically don't use manual focus anymore, something that the L s are much better made for.
I think I'm in the minority of people on CR who don't have Elle's Disease. Good job really 'cos I have a disease involving long faces, tails and four hoofs