I reviewed a paper but was not informed of the decision -- is this common?
While most the journals that I have dealt with inform me of the editors' decision, I have found that a significant minority do not.
I've found this to be the case in fields with significantly different publication practices (e.g., computer science, biology), so I don't think it's field dependent. Likewise, there seems to be little consistency in which journals allow me to see other reviewers' comments and which do not.
My guess is that hiding review or decision information is some sort of attempt to increase editorial independence, e.g., allowing an editor to more freely decrease the weight given to an unfair Evil Reviewer #3.
I really do not like it, however, since seeing the editors' decision and the other reviews helps me simultaneously evaluate the quality of the journal and editor, which are also quite important to know (and sometimes give feedback on).