Some people have found this wording to be somewhat objectionable, but our clients appreciate it. People have said things like, "What if I send you a response to a USENET article, that you didn't ask for? Is that unsolicited?" Our answer is no, we're not talking about mailing a topical response to a public post, we're talking about gathering someone's e-mail address and tossing it on a list which people use to mail out stuff totally unrelated to, say, someone's post. Or if someone visits your web site, and looks at it, and clicks on your mailto: link, and sends you mail that says "Nice web site!", well, fine -- but if they make a note of that e-mail address and later use it to mail you something totally unrelated that you never asked for... that's mail you never solicited. This means if someone looks at my web page and says, "Hey, she used to live in Peru, I'll just add her to my mailing list for talking about tourism in Peru!" that's uncool -- though they could certainly drop me a note and say, "Hey, I just found your web page when I did a search for Peru, and I noticed you used to live there, and I have a web page I've put up with links to pages of people who used to live in Peru, would you like to be on it?"
FWIW, an example would be the time that I subscribed to a mailing list about Peru, and that was cool, but then for some strange reason, I started getting piles of mail from some other address in the same domain as the list to which I had subscribed, and the messages were all Word 6.0 documents which I couldn't read, and looking into it, I found out that everyone on the first list had just been added to another all of a sudden... this is attributable to general cluelessness, and it was well- intentioned, and a bit of talk about this cleared things up, but IMHO it's important for people to generally be aware that the existence of an e-mail address doesn't mean it can be used without someone's consent, and I'd hope to see consciousness raised in that respect.
While the bulk of unsolicited e-mail does tend to be commercial, there are some instances that aren't strictly commercial, and I feel it's of some value to argue this point in a manner that doesn't have so much to do with what's in the message as it as to do with how it ended up in one's inbox. This means if someone gets subscribed to a mailing list without their consent, they haven't solicited the e-mail they received as a result, for instance...
Well, anyway, that's my soapbox moment about the term "UCE"... I feel fine about "Excessive Multi-Posting" for instance, but I'm not overfond of the term "Unsolicited Commercial E-mail."