Mark,
There is certainly a recency effect for me as well. Of courses that give me really good first impressions, I find that about half of them having staying power and the other half drop a tier or two over time. Sometimes the good vibrations last a few weeks, other times a few years before the slide. When I first played them (and before I added a number of the courses now listed), Wolf Run was my #2, Paa-Ko Ridge #3, and Chambers Bay #3. On the other hand, Victoria National started at #15 in 2009 and has moved up even though seven of the courses ahead of it now were added later. Paa-Ko is the one course I've played quite a few times now--I still like it more than most do but the mountain scenery is admittedly not quite as spectacular after awhile.
Tom,
I think Golf Digest would probably prefer that panelists not ever rate courses together--which is a bit different from GolfWeek and their rater outings. Its hard to avoid entirely--I have too many rater friends at this point. But I think we make a point to never discuss actual ratings.
I do think there is one positive that comes out of discussing courses with others (not the specific numbers) and that is that it often forces me to justify why I like or dislike a course. Most of the time I have pretty specific reasons and can articulate them, whether or not the other party agrees with me. Every once in awhile I hear a point I hadn't noticed or considered previously. For one course, a poster here made a point that a certain course had very little variety in the sense that almost every hole was mid-length, including 3's, 4's, and 5's. When I went back and reviewed my notes and the scorecard, I found it to be true, even though I hadn't noticed it on my actual playing of the course. I would say that type of thing is pretty unusual, for me at least.