I serve my blog via my dinky 128kbps upstream DSL link, so bandwidth is precious. Fixing the fiasco of mod_gzip triggering an MSIE bug helps a lot. Now I'm supporting If-Modified-Since and ETags headers on my blog contents, too. The magic is Bob Schumaker's lastmodified plugin, which pretty much Just Works. Thanks, Bob!
Please tell me if you see any caching weirdness.