Help for methods
See the .helpForCall function in utils. It would recognize that the function was an S4 generic, and then work out the signature and look for matching help. I think working out the signature in the case above would require it to call lm(...). So there's a precedent for what I called a "huge mistake": maybe it's not so huge...
And I'd imagine, in practice, most people would be doing something like x<- ... ?summary(x) so that wouldn't have to do an extra computation. Hadley