Proprietary periods are nothing new, and provide a balance that helps observers out while preserving the openness of science in the long run. The complaints from the community stem from an extension of the proprietary period for the Kepler team that was granted in April. All of the data were set to be released this month, but the extension is until February 2011.
Today's partial release has re-ignited the debate. Some critics claim that the Kepler team is being too conservative.
To be fair, however, with all the data rolling in, is it not best to be conservative and limit the number of "false positives" that creep out? Also, in announcing the presence of an Earth-like planet to much fanfare, you probably want to be darn sure of what the data sets are telling you.
More eyes on the data could be a good thing for the search as a whole, but I think that NASA still has to be concerned for the careers of the scientists, and presumably students, working with these proprietary data.
Knowing a little bit myself of what it is like to work with a budding instrument from scratch, it would be disheartening to not have enough time to publish results before someone else got to work with the data. So, maybe that's why I have sympathy for the Kepler team.