I'm not arguing against the rejection, but I want to mention a point in relation to Raymond's statement "five levels have sufficed for a long and that the need for finer distinctions almost never arises in practice".  In thinking about my own codebase, I have only one project where I added a notice level, and none in which I currently have a TRACE level although I think I used it as described below in one during development.

If logging had had TRACE built in, I would have used it in almost every project I've written.  Instead, I squash everything into the DEBUG level, and that results in two things: overly verbose debug logs, and still having to go in and add extra temporary debug logging statements to debug hard problems.

I don't think this is a terrible thing.  The "pain" of it only once rose to the level where I added a TRACE level to my program. My point is that the lack of TRACE (or NOTICE) getting added to projects on a common basis, rather than meaning the need for the distinction "almost never arises", means instead that the need for them is less pressing than the small pain of adding them.

I will make one argument in favor of adding a TRACE level, but I don't know that it is enough to shift the balance.  That argument is that if I had a TRACE level built in, instead of adding and deleting extra temporary debug logging statements during a debugging cycle, I would add them at the TRACE level and *leave them in*, at least until I was ready to ship the code.  Not having to add and remove them, and then almost always end up re-adding and re-removing them, would speed up my debugging cycle by a non-trivial amount.  Why don't I add a TRACE level and do this?  It feels like too much of a pain "just to debug this", but then I wind up coming up against that decision again when working on the next bug, and the next..and each time it is too much of a pain to add TRACE "just for this bug".  

So, having TRACE built in might speed up debugging cycles, because programmers are lazy :)

Having made this conscious as a result of thinking about this issue, I may start adding TRACE to my projects more often :)