Cattlegrids
If you out in rural areas watch out for cattlegrids
I've been training a fair bit on the Brompton recently, I did 40 miles from Garstang to central Manchester over Belmont in 2 hrs 40 mins - I don't know how that stacks up against a conventional road bike...
Other things I've been considering are how fast should I let it go down hills? Obviously where it's safe etc and also whether the Brompton can take hard "out of the saddle" up hill climbs? So far I've experienced no problems but then I'm still fairly new to the bike.