Hello, first post. 
I recently switched from Windows to Ubuntu and stumbled across Synfig in the software centre. I installed it on a whim, thinking it was for basic gif animations but was pleasantly surprised once I realised you could do full cartoon animation with it.
I had done a few animated music-videos for my electronic-music with Macromedia Flash years ago. What I like so far about about Synfig is all the advanced tweening capabilities (especially all the parabolic waypoint stuff which is a lot like synthesizer envelopes in electronic sound design… but I digress 
). Tweening is what made Flash a time saver over traditional paper-based animations methods for me but Flash has a lot of web design features which were irrelevant for my purposes.
So Synfig is really up my alley and I am currently working my way through the tutorials.