Good important point encyclo, yes it does help to mention that.. (sorry my bad, I forgot that;) I test in both cases by default hehe) Yes that narrows the focus too, you know even if you're not using one, mention that too!
yes the well known ones are fine, as long as the resource is is authoritative, unique, tried and tested! A general "rule of thumb" for what's not allowed = no "blogs" or web design companies.
Reasoning: Around these forums everyone has them. Singling out one is bound to be a conflict of interest to our Members. To avoid grey areas between what might be self promotion (intentional or otherwise) and what is tried/tested facts, and to protect the integrity of WebmasterWorld policy in general they have to be avoided. Quote from TOS#13 [webmasterworld.com]
Again Moderators can and do discuss/use their judgement in exceptional cases (e.g. new groundbreaking, techniques) so if you're unsure just ask..
If a URL is filtered it is likely someone did something that earned them a place on said filter.. See this thread [webmasterworld.com] for more info.