If you want to follow someone on Twitter without signing up to the service yourself, getting updates via RSS can be useful. Twitter's December redesign got rid of the visible RSS feed option that used to be there, but you can still add individual Twitter streams to your news reader of choice.
Stackoverflow points out that the RSS address for any given Twitter user is in the following form:
So for Lifehacker's Twitter feed, the address would be
Handy if RSS is your prime way of keeping up with stuff.
RSS feeds in new Twitter [Stackoverflow]