Hey hhk – SlideDeck just put up a new pricing page: https://www.slidedeck.com/pricing
I think it is pretty straightforward what you get, they also have some posts in Get Satisfaction that explain the differences, here’s one:
https://getsatisfaction.com/slidedeck/topics/difference_between_free_and_pro_versions
Their WordPress plugin is a more simplified version of their jQuery library. Most people don’t even bother with making a WP plugin in addition so I give them props for that.
From what they say in GS, right now the big difference is the removal of the bug & touch support but Vertical Slides are coming soon to WP PRO, and as they stated, the WP PRO version will have access to future features.
I think it is a great plugin, imho