Well, I moved to Madrid back in April and have been driving since early July.
The drivers in MAD are nuts and you need to be careful. Speeds are also quite high. ALso, remember that most rental cars will be stick shifts (manual) so know how to drive one or be sure to reserve an automatic in advance.
The roads, at least the main ones, are pretty good.
I'm going to drive MAD-Zaragoza-Barcelona-Valencia-MAD when I go on holiday (¡in 2 weeks!) so will be better able to give details when I return.
Traffic in August along coastal roads is horrendous, so add lots of extra time to your drive estimates.
------------------
I Love New York -- Viva España