My 2cents on the balance/donator issue:
I don't see how it won't be activity limited in a practical case anyway... Granted we haven't seen the progression for ourselves, but if, as Zen says, it takes roughly 250 days to get to level 7 in a skill with no advantages given for current intelligence scores (i.e. the progression is the same for all) this is really no different than the careers. You can complete all the courses in school needed to get that 7 INT in less than 250 days.
In both cases (careers and skills) there is no advantage being a donator while progressing:
1) there is a cap to the amount both can be worked per day, so the donator refresh does not come into play.
2) Neither can be gained faster due to donator status or stats
3) At least for the first 8 months, no credits are needed to advance in level. I am sure something will change before then anyway.
4) How many people currently have a career level past 7 anyway? 20? 50? with the variety of skills, several people will chose to have both knowledge and combat skills anyway.
I haven't been around as long as some, but it does appear that Zen has carefully thought out the balance aspects in a lot of areas of the game. Of course there are advantages to being a donator, but they are not universal and the game is extremely playable without being one. However, if you want to become the next Ush, Pun, Pullo, etc there is only one way to do it in less than 5 years. 99% of us can't/won't go there, but is fun to play anyway