Querying etiquette?

So today I attended a writing seminar, or at least part of it… namely the section on “getting your work out to other people”, and naturally a part of that was talking about agents.

A question came up about sending to multiple agents, and the response was in no uncertain terms, NO.  We were told that sending to multiple agents was a huge faux pas, not to be done, a mark of unprofessionalism, etc., etc.

Now, this didn’t sound right to me, but I held my tongue.

So I put it out here: unless an agent asks for exclusivity, they don’t expect it, right?   A query isn’t a commitment, it’s… just a query.  You can send them out to five or ten or a hundred agents at once (smartly, of course… no “Dear Insert Agent Name Here”), and it’s not a big deal.

Or am I wrong?  I’m perfectly willing to admit I could be.  I’d love some insight here.