It's great, all programs on my computer these days think they have to automatically check for updates whenever they are started or sense that a connection to the Internet has been established. I usually don't mind and even welcome it. However, there are situations, especially when I use volume restricted wireless 3G access such as Vodafone Websessions, in which I don't want those multi-megabyte downloads. So I've switched most update services to semi-manual or manual to control this behavior. But even this sometimes doesn't stop the talkers.
Recently, the Windows update service told me it wanted to download a 30 MB .NET update. Sure, no problem, I was at home at the time, so please go ahead I thought. However, it didn't as there must have been a problem with the update service. So the originally agreed update only started a couple of days later when I was abroad, hanging on a thin line. No way to stop that 30 MB download, no task revealing itself as the culprit that could be terminated, no nothing... Ugh, I was angry.
But here's the solution in case you have Windows Vista installed: Go to the firewall configuration and set the profile which is used for dial-up connections (in German it's called "Öffentliches Profil", that's probably or "public profile" in English) to block all "outgoing (TCP/UDP) connections". Then go to the outgoing rules section and create new rules which allow only the programs you like such as Firefox, your eMail program, etc. to establish outbound connections. In a last step, assign these rules to the "public profile". No more nasty connection requests and update dialogues while you are away.