This is an awesome plugin and I use the free version because I installed it for a (still unfunded :-( ) charitable project. Now I found on your website about the paid version:
Changes in WPML 2.1.0
17 critical bugs fixed.
3 security holes closed.
(while I use only the latest free version 220.127.116.11.)
My question now: Is there any serious lack of security if I keep on using the free version, since the mentioned 3 security holes have been closed only for commercial versions, and do you recommend to upgrade for security reasons? Or does it not make any difference in terms of security?