Indeed, it has been widely noted that craigslist's authenic feel (hyped by the .org TLD) and community fostering ruggedness has created a cult-like following. It seems that their lack of graphics, change, and heavy UI development has kept the installed user base, well, installed, and growing.
http://www.startupnation.com/pages/newsroom/PR_2006_0128.asp
'... lack of graphics, change, and heavy UI development ...'
this is also a cheapskate way of concentrating on the development & lowering costs. Such cutting edge (performance wise) technology reminds me of the Mercedes Benz silver cars ~ http://tinyurl.com/2ufx36 ~ so called because they stripped back the paint to save pounds to enter Le Mons. In this case stripping back graphics to allow good scaling.
Thanks for the link.
From memory CL currently runs on about USD20 Million / year gained form paid adverts. No fancy designs, just the data.