These days with anti spam measures it's a must have in fact. I'm a hoster myself and we limit the outgoing emails at 500 per email address. Per day!
Exceptions can be made, but we are not eager to do this as these days also birthday messages get reported as spam. Unbelievable that people don't even like a birthday message, but this do gets servers into those dynamic blacklists with hotmail. Which is not nice for other customers on the servers.
Also lots of mails per minute to the same provider, like hotmail and gmail can get you on their grey or blacklist.
I also remember there were limitations for that in vBulletin, so I'm going to convert to Xen (from IPB) in januari and +1 for this.
Just a must have theyse days.