claus - 4:33 am on Feb 8, 2010 (gmt 0)

Why would this be "spammy", I wonder?

I don't see the spam in this. It's a normal feature of most/all blogs, and as mentioned above completely natural in breadcrumb systems.

Do we see blogs and sites with breadcrumbs consistently at the top of SERPS? ... not really, IMHO

Although I like the idea of a "high rank shortcut" just as much as everyone else, I would look for the reason for your higher rank somewhere else ;)

--
Added: It doesn't have to be on-page; it could also be off-page/off-site factors. For that matter, it could be that some new filter hit your competition and missed you