After having a slew of trouble trying to arrange a Mexicana flight to Cuba for May dates, I'm thinking of going in December when the Film Festival will take place Dec 4-14. Has anyone taken in this event? What did you think? Would the weather be less hot than in May? Are the films free or not? How much more does being in Cuba during December cost than during low season? Please excuse these basic questions but I live in Mexico and don't have a Cuba guidebook.

Consider arriving a few days early and take in the international music festival Jazz Plaza (29 Nov - 2 Dec). The best Cuban musicians sharing the stage with foreign guests: great diversity, highly recommended! However, concerts are NOT free (10-20 CUC for foreigners), neither are the screenings at the film festival.
December temperatures will probably be slightly lower than in May - not an issue to worry about, IMHO. The first half of December is not yet high season, and Cuban prices don't differ very much over the year.
Why not invest in a good guidebook? I suggest Moon Cuba, Lonely Planet is also useful.
Ahh - good tip, LowlyPlant, about coming early for the Jazz Festifival. I'm planning for my next trip to Cuba in December, both for the relatively cooler weather and for the film festival. So raquelita, if I come across any useful and helpful information I'll pass it along to you too. I have been looking at the website - www.habanafilmfestival.com</a> - but my Spanish isn't good enough to know if I'm missing something relatively obvious about ticket or pass prices.
I'd also recommend a guidebook to peruse while you're planning. I read that you lived in Oregon ... you should order from Powell's!
This Time Out guide was one of my favorites because it's small, so it's the one I brought along with me.- it focuses on Havana. If you're going to venture beyond Havana, you might want another one as well - though this one does cover a lot of essential information on most other locations ... also, looks like there's a 3rd edition coming out soon, so you might want to order that one instead.
I'm a book junky, so I bought several and read them all before hand, and just took the small one to have a few basic bits of information on hand. I almost went without one at all, thinking my research and the notes I'd taken would be enough, but that would have been a mistake. I'll keep an eye out for some useful tips for other folks who've been to this festival before - and I'll be glad to pass along whatever I come across to you too!

thanks to both of you who've responded. After reading your comments, I'm going in December. One extra advantage is that I'll have time to get a guidebook.

Neither has told you about the film festival. While music and art festivals are always entertaining, they are interesting even if they are very limited in their content in Cuba (I was at the Havana Jazz Festival in 2004). Be prepared for last minute annoucements of gigs and since these events are geared for tourists, unless you know Cuban artists, nothing is free.
The majority of your interactions will probably be with other film tourists.
Prices are 2-3 pesos (Moneda Nacional). Interesting queues on basically all films and all cinemas. A film newspaper is printed everyday (or every other day, don't remember now) with all the films and cinemas they are shown at. Cubans (at least in Havana) are crazy about cinema and long for this festival all year.