They now have unlimited storage for free but there is a 1MB size limit on individual files. I did subscribe before when there was a limit on the number of photos you could store on the site, but the updated free version suits me fine now.
They have an iPhoto plugin which means its a doodle to export from iPhoto so end up having all my photos backed up on Photobucket. Also very easy to post photos in forums or on Facebook as the appropriate links for individual photos or whole albums are easily copied and pasted, or shared.