Hello,
I have rented vehicles in Spain for eight (8) years in a row, soon to be nine (9) in September. I have never been required to have a IDP. I have rented thru Hertz, Avis, Dollar, and Auto Europe. My Massachusetts drivers license is all that has been required. Additionally, I have been stopped at random police checkpoints in Italy and Portugal and again my USA drivers license sufficed. I am a AAA member and I used to obtain International permits for my European travel, however it was more of an inconvenience as they are only valid for a year and on top of the permit fee they charge you to have your picture taken.

mike - so you advise not wasting money on IDP - I think the many reasons above for getting one and it is a legal requirement or fulfills one so still advise not getting one?

<<I have never been required to have a IDP.>>

Oh yes, you have. It's the law, which means it's a requirement. What you meant to say was that no one ever asked you for one. BIG difference.

The rental agencies may not have asked you to show an IDP. You often do not need an IDP to RENT a car, but you do need an IDP to LEGALLY DRIVE. AAA only charges for a photo if you don't provide one.

does seem like IDPs should match drivers license validity period - a year though is fine for most. After many long and at times heated discussion here consensus was that IDP is a legal mandate though often not checked by rental agencies or cops but still some have been fined -in Spain where you also are legally required to have a spare pair of glasses with you in car at all times driving.