Advisor Takes, Postdoc Gives: In this scenario, the advisor is looking for a postdoc who is already a demonstrated expert in subtopic Q. By bringing this postdoc into the lab, the advisor will be able to capitalize on the previous knowledge of this postdoc and glean some “easy” training on subtopic Q for other students in the lab. I imagine this is a common situation in the labs of assistant or associate professors who are interested in branching into a new area of research with which they themselves are not particularly familiar. This is great for the advisor, but perhaps not so great for the postdoc (unless s/he hadn’t gotten enough of his or her grad work and wanted to do more).
Advisor Gives, Postdoc Takes: In this case, the postdoc has a general interest in the work going on in the advisor’s lab, but little to no previous experience with it. Typically, the postdoc has previously demonstrated some excellence with subtopic N, and the advisor trusts that the postdoc will have some fresh insights into subtopic P. The postdoc requires a significant amount of ‘start-up’ time in the new lab, as it is difficult to digest an entire new body of literature overnight and suddenly spew forth unique and/or head-spinning ideas. Such a circumstance can arise in a variety of labs, but usually occurs under the tutelage of an advisor who is simply interested in good science and doesn’t have a burning need to delve into any particular sub-discipline. If the postdoc is smart and creative, this is probably a win/win situation.

Too Much Attention: The advisor is either overly excitable, overbearing, or obnoxious. This kind of relationship should be completely unnecessary at the postdoctoral level, since one of the major goals of a postdoc position should be research independence.
Happy Medium: This advisor has a vested interest in the postdoc and enough time to be available for mentoring, when needed. Most likely, this advisor manages a medium-sized research group (say, 10-15 researchers). The postdoc has enough freedom to plan his or her own experiments, but can approach the advisor when additional advice or input is desirable.
Advisor? What Advisor?: This advisor is so busy and/or manages so many people, the postdoc has little to no opportunity for regular interaction. In this scenario, the postdoc is left to fend for him- or herself. This situation may result in a highly independent and capable postdoc, or it may result in a postdoc that wallows in indecision and regularly cries him- or herself to sleep. Get out of the boat. Sink or swim.