I’ve always found Bing an enigma. I have pages that rank well for keywords they are totally unrelated to, while the pages that are 100% on the money for those terms are know where to be found. They are still a long way behind Google in search relevance. Their webmaster tools is a joke compared to Google WMT. Just a far less sophisticated product all round imo.
Trouble is, now that they also power Yahoo all of a sudden Bing search has a share of the search market that can’t be ignored. SEOing for it is like throwing darts at a dart board though.
One thing that I have found has helped is site-wide 301 redirects from non-www to www. Bing seems to struggle more with canonicalization than Google
As for the smaller engines…waste of time worrying about them other than the general principle of pushing out quality content