"inktomisearch" (yahoo crawler?) how much is good

..how much is bad?

I've read that some people had that crawler visit their site a lot, and took a good deal of bandwith.

They're not recent articles (2003-2004) so I don't know if it's different now.

But I noticed that inktomisearch shows up on my website a few times or more a day. It says there's a guest but when you check the ip it is inktomysearch, sometimes an msn bot, etc.

I'd like to know if there's a point at wich these things become a nuisance, and also, why the frequent crawls?

What do you do if they become too bothersome?