Is there a recommended size for a presentation?
Nope. Anything goes, as long as the machine you present with can handle it.
I wouldn't go over 75 MB for any single file, however.
and maybe
a suggested size for sending via e-mail? I am sure that
those two sizes could be extremely different.
Yes they are. Some mail servers can't do files bigger than 5 MB. In any
case, I'd never send anything over 500k before asking the recipient if that
size is OK. You never know what happens if you send a 12MB file to someone
with a dial-up...you kinda hose up their email system for a couple hours,
minimum.
Business-to-business is a bit different, in that most have broadband. You
can send them bigger files.
John O