Having just read through the thread ...
1 email that may be relevant to the company asking them to opt in is acceptable in my opinion ... once they don't opt in ... remove them from your list ...
I hate spam ... in both kinds email and snail ... I do however actually look at the spam mail I get in through my letterbox ... from a design point of view ... as well as from a ... something free point of view (whether its 20% off something or similar)
Spam I get into my inbox ... I check if there is some text in there ... if its just an image it gets junked immediately ...
I don't consider ... viagra / perscription drugs / date me / free personals or social network signups to be valid unless sent by an actual friend I know
I guess however I'd draw a fairly fine line over what is valid and what isn't
...
as a developer / graphics person .. I'd be curious about graphics packages and developer tools ...
However if I was getting asked to join a forum ... I'd consider it spam ... as I got asked today on a forum and reported it accordingly