Really depends on how you plan to use it. Keep in mind that this product is so light, and the battery lasts forever, so you may take it with you everywhere. In that case then 3G is with it. In my case, I work in an office, and rarely am not in wifi range, so I opted to not buy the 3G, and I am very happy.
I think the 3g is 100 % worth it.. Not all programs will work offline (as of now, some are in the progress of being made able to work offline). So with that being said, the 100 MB of free internet on the 3g version is worth it to me to purchase the 3g version.. Normally i use wifi so I have never came close to using up my 100 free MB. If I know I will need more internet I jsut purchase 1 GB at a time..