Interestingly, in Spanish one never says "at" (or its Spanish equivalent..) for @. It is called an "arroba," which is also unit of measure (for both weight and liquid) that I have never heard used - my Spanish dictionary says it varies in weight from 24-2- to 36 pounds, by region, which would explain why it ain't used much.

There seems to be a parallel here, with these odd typographical symbols given names having to do with weight (# and pound and @ and arroba), perhaps because they were used as shorthand for the units (as when one sees a weight as 20#).