Not really... the word "hosts" might be misleading. Gnutella works this way that, whenever you connect to someone, he tells you about all the other people who are connected to him. This way you get an ever increasing list of gnutella clients (or "hosts").

There are some computers who will store large lists of systems online at the moment, to get you started in the first place. Moak has posted some of these recently here ... I can't really remember the exact adresses (call me Captain Alzheimer), but basically if you can get a connection normally you won't need to enter anything into the host files.

Only other situation I can think of, where you might want to still enter an adress is, when you know that a friend with a gnutella client is online and you know his IP and you want to connect to EXACTLY him...