I think the 'best nodes' idea, whether it be of the day, week, month, or year is conceptually a good one. It would be nice to be able to come in and skim 'the best' when one is in a hurry but I see two potential hurdles to the success of such a section.
The first, being that reputation would likely be the only viable method for establishing placement into the category. We have all seen nodes that contain very little of substance that otherwise get a reputation boost either based on a witty comment, the author's status, or simply by being on the frontpage. While they may have been good posts worthy of the reputation earned, I hazard to guess that is not what many of us are envisioning as 'best nodes'...perhaps like the XP system, the good would generally rise to the top most of the time and this could be acceptable.
Second, I wonder how a nodes placement into such a 'best nodes' category would artificially affect the reputation of that node? We already have many who push all their votes on the frontpaged nodes in an attempt to use up their votes and gain some XP. I suspect a 'best-nodes' section could end up being used in a similar manner....this might be alleviated by not being able to vote on the nodes listed in the section but requiring the user to click on the node and bring the entire thread up before voting.
Of course, I still like the concept, but I think it needs some thought in order to be done properly.