Some IRCd's rate limit remote commands. I've only tested these two:

freenode (ircd-seven):

whois KindOne KindOne
:tolkien.freenode.net 263 EvilOne WHOIS :This command could not be completed because it has been used recently, and is rate-limited.
:tolkien.freenode.net 318 EvilOne KindOne :End of /WHOIS list.


EFnet (ratbox):
whois KindOne KindOne
:irc.underworld.no 263 EvilOne WHOIS :Server load is temporarily too heavy. Please wait a while and try again.]
:irc.underworld.no 318 EvilOne KindOne :End of /WHOIS list.]


//uwho KindOne KindOne
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irc.swiftirc.net #msl (mIRC Scripting Language)