I wouldn't want to see the Offer HN thing become a lasting trend at the current levels... that said, the odd "Offer HN" doesn't bother me, and I certainly wouldn't want to think that all offers stopped completely just because my post got upvoted.
That said, to elaborate on the point jacquesm singled out, many/most services-businesses (from tax consultancies to seo consultants and web developers) use free consultations as a way to generate leads. My suggestion to people who want to offer something to HN is, don't do it just to generate leads, and try to make it clear to the readers that it's not something you're doing to generate business for yourself. It'd be a shame to see some percentage of this site become basically a lead-generation site for the brazen few willing to take advantage of it like that.
PS: I'm not suggesting that any specific "offer HN" post was like that, despite mentioning examples above.