Being able to post comments in online documentation is one of the greatest inventions since sliced bread. No online document should be without this feature. Adobe does indeed have this feature on some of their online documents (e.g. stuff on developer.omniture.com) but not on all of their other documents (e.g. Adobe Analytics and DTM docs). My suggestion is to add ability to comment on the document pages for all of your online documents.
Namely...
DTM http://microsite.omniture.com/t2/help/en_US/dtm/
Adobe Analytics http://microsite.omniture.com/t2/help/en_US/reference/
Adobe Target http://microsite.omniture.com/t2/help/en_US/tnt/help/
..snce these are the most often implemented things.