During the first year of finishing my FFR, I drove mine to work 2x per week in addition to the weekend. Of course rain would stop that, but we get rain about 2 months of the year in total. The first year, I put on nearly 5,000 miles.
I built the FFR to be as reliable as a daily driver would have been back in the 60's and 70's when Ford still built carburated motors. It never crossed my mind that if the engine is built with care (i.e. correct torque specifications on all bolts and all tolerances adhered to) that there's no reason it couldn't be a daily driver. My 65' Mustang is a testament to that, which I drove as a daily in my college dazes!
The one time my car quit on me (momentarily) was an electrical issue - just had to tighten two screws and I was back to working again. Engine-wise, it's never let me down after 17,000+ miles.