there are very few good mambo/joomla websites out where. i think they (mambo/joomla develpers and users) just boast about mambo/joomla. the big problem here is the performance. slow mysql queries are one of the culprits. i am waiting for mambors to take off, i think mambors may offer some hope in resolving the performance issue. also if mambors has good performance, then i hope it will replace mambo/joomla.
any good content-rich website has thousands of pages, which curent mambo/joomla can not handle at all.