I have no objection if someone who honestly saw a message I wrote and thought I'd be suitable for a particular job emails me asking if I'm interested. However, the same email would be bulk if sent to everyone who posts to NANOG, even if says, "I saw your post about "Re: Fwd: Re: Digital Island sponsors DoS attempt" and thought you might be interested in buying our premium fishing worms".
A corallary to this is the dreaded "I saw your resume on <insert job board here> and so you must be interested in our offer of <insert job hunting service here>." The spammer would argue they are in the right, in that as part of posting a resume, one is expecting, and inviting responses. However, I would argue that just because I post my resume, doesn't mean I'm interested in anything other than serious job offers. I dealt with a similar situation from the abuse desk end, in which a client was doing searches of resumes on job boards for a given skill set, and then mass mailing them with a specific job offer that centered around that skill set. It was a tough issue to resolve, because on the one hand, from our client's perspective, he was contacting people he thought would be genuinely interested. And yet, from the recipients perspective, since it wasn't directed straight to them, it could be considered UBE. Moral of the story is, it came down to a very fine line of what does "solicited" mean? We ended up comprimising that he would fully disclose where he got his email addresses from, and why he was sending the email, which all but competely eliminated complaints. Scotty Allen