so our frommer's provence guide which we bought last month said said march was a good time to go (in fairness, they say sept was their favorite time, but clearly say March is in the 'good' window of time to visit)
i'd have to strongly disagree with March being a good time to go. certainly, it's quieter in march. but.....
much of provence's charm are the trees and tree-lined streets and promenades. without leaves, it looses quite a bit of it's charm
if i had to do it over again and wanted to go in spring (to avoid the summer high-season), i'd go in late april, maybe early may.
the other issue is that in March, there are still some restaurants (or other locations, such as a wine cave Lourmain) may not be open (from their winter hibernation). or if they are open, you may be the only one there. although i like to avoid tourists when travelling, eating in a almost empty restaurants is.... i don't know... a little weird. unless you like that sort of thing :)
lastly, there was a recommended restaurant in our book in avignon that the meal wasn't great. i believe the name was Hiély-Lucullus.
the meat was very chewy. definitely not what we expected for one of our more expensive meals in france. maybe they had an off night. maybe their real chef only works during tourist season? who knows
yelp.com seems to become more popular in france now so before you go or while you're there, i'd cross-check places with yelp (i have an iphone with sprint. i'm in san diego. as long as i had wifi access, which was everywhere, there were no additional fees from sprint to use internet to use yelp and google maps!