Current practice:argument types in function declarations

[masinter.PA@Xerox.COM]

The cleanup committee is considering various issues surrounding function
declarations, and, in particular, declarations of the types of arguments.

We've had considerable input about what such declarations could mean, should
mean, what CLtL says they mean. Rather than going over all of that, this is a
question about current practice: 

What do current implementations actually do? What do current users actually use
have in their programs?

Is anyone aware of any (released? supported?) Common Lisp implementation that
pays any attention at all to the types of arguments, e.g., for which

(proclaim '(function my-function (list vector) t))

has any effect different from

(proclaim '(function my-function (t t) t))

?


Does anyone *have* any Common Lisp code which contains such declarations? What
is the intent of the declarations, other than as documentation?