I am very lucky that I have only ever used a wheelchair once before in my life when my leg was in a cast, but the side effects of chemo meant that for a few weeks I needed to use a wheelchair when out and about as I couldn't walk far. I have had some interesting experiences whilst using it.
My Mum pushed me the majority of the time, saving my arms, but we have hit things in shops that maybe don't consider the width of a wheelchair quite enough. Lifts are usually available in shopping centres etc. but they don't think about making them large enough to turn the wheelchair around whilst in there so it can be pushed out forward rather than being struggled out backwards and perhaps into the path of other people.
Dropped kerbs sometimes weren't quite dropped enough either, meaning we had to reverse over some so that the larger wheels could negotiate it. Once we parked in a car park that when we tried to cross the road from it, we realised the kerb wasn't dropped opposite it, and rather that it was dropped 150m further down the road. This meant I had to be pushed down the middle of the road, with my Mum running as fast as she could behind me: not exactly ideal.
As much as I'm sure disabled access has improved over the years, from my short experience I've spotted several things that just haven't been thought through properly.