Apparently there are going to be five series'. So I have given up watching it now because I cannot be @rsed for another three and a half series' to wait to find out what is going on.
** POTENTIAL SPOILER** I've just heard from a reliable source (!) that they are going to finish the show with series 3. The first four episodes of series 3 will be screened in the US in September 2006 and will focus on explaining who the others are, how they got on the island and why they needed Jack, Kate & Sawyer. As I say, this is from a reliable source!!!