I see no disadvantages of upgrading, especially from OS 3.1, OS 3.9 is like a totally different Amiga OS. :-D
Amiga OS 3.9 came with my Amiga 4000 preinstalled, however I wanted a freshinstall and unfortunately lost the 3.9 that was on it, however I have 3.5 installed, I miss 3.9, I need to buy it soon... if I get some money. :-P
Yes, 3.9 is VERY much worth it!
