In my somewhat limited experience with my 32' long motorhome, it hasn't been too much of a difficulty, though of course it is harder than with a car. I basically need two normal parking spaces end-to-end lengthwise, or a strip of perhaps a half dozen side-by-side. In smallish towns and suburbia, this isn't too difficult to manage. In big cities...well, I plan ahead to avoid the problem by camping close enough to public transportation to be able to use that (and otherwise generally avoid driving through the heart of the city).
Naturally the details vary a great deal with what specific town you're talking about and on whether or not you'll be towing something. On the other hand, I don't think the precise length of the motorhome makes as much difference for parking once you generally can't fit in a single parking space.