What constitutes publication?

If a poem has been selected by an editor and "published" in print or electronic form, then I would consider that poem to be published. Printing a poem in an online journal obviously makes that poem "published". Posting a poem to the poets.org forum, although it may be read my many readers, does *not* constitute publication—in my mind, at least. That's because it's equivalent to tacking your poem up on a notice board at a college campus or wherever. The key to this discussion (although not the only concern) is that on the poets.org there are no editors. There is no virtue or necessity to "acknowledge" such appearances of one's poems. It's like acknowledging the notice board to which you might have thumb-tacked your poem. Why on earth do that and consider it a legitimate acknowledgment?

I have to disagree with the idea that anything accessible online is considered 'published'. Poems or articles posted to a blog for instance are not considered editorially to have been Published (although they have, legally, been published—note the distinction of the two by capitalization or not of the initial P). Similarly for posting by authors on their own or on an employer's web pages.
Think of pre-prints—if pre-prints of a book or article are made widely available or disseminated, they are still techinically not "published", despite being easily had.

I think the discerning factor here is the idea of peer review. It seems, then, that author intent is one key to Publication (as opposed to publication). A paper is considered Published when the author submits it somewhere for Publication and it is accepted, but not necessarily when it is made available for consumption.

The expert and the neophyte both have equal voices on the internet. Thus it is up to each person who reads information (including poems and commentary about them!) online to take it with a great grain of salt.