I have been riding an aluminium frame hybrid bike for 20+ years and it is coming to the end of its life. Having tested a couple of carbon hybrid bikes and been very impressed with the responsiveness of the ride I'm considering taking the plunge - something like a Canyon Roadlite or Trek FX tick most of the boxes. It will be used primarily on my short (5 mile) but hilly commute, as well as longer weekend rides.
I've read several posts that discuss the fatigue and impact resistance of carbon frames vs aluminium vs steel, and I have a couple of specific concerns that I haven't found addressed in detail elsewhere:
I am concerned about possible damage caused by securing a carbon frame with a D-lock (== U-lock). I store a pair of D-locks at my workplace where we have semi-vertical bike racks. I will not be mounting the locks on the frame. However, it was suggested both by a mechanic in my LBS and Canyon's online chat assistant not to let the lock rest on the frame. This is suprising - each lock is insulated with thick plastic and weighs perhaps 1.5 kilos. I thread one lock through the front wheel and let it rest on the down tube, and use the other one to secure the back wheel to the stand. I wouldn't expect a carbon frame to have any trouble bearing a small load such as this, as long as there is no forceful impact when locking/unlocking (or of course from accidental damage from others removing their bikes). From what I've read it takes a major impact such as a crash or forceful hits with a hammer to cause impact damage.
I've read a few posts suggesting carbon bikes are less suitable for commuting for several reasons (harder to fit racks and mount locks; more alluring to thieves), bit also due to the weather conditions they will face. As I'm based in the UK there will be no shortage of rain and roughly half my commute is on roads. Road salt is known to corrode aluminium over a long time, but are there similar concerns with carbon, or is it just people being more protective of carbon bikes because they're more expensive?