They claim the Maya calender ends on December 21st 2012. So whats the big deal ? Calenders do need to have an end. In fact every thing do need to have a beginning and an end. The Maya calendar starts from 3114 BC . Does that mean that the world started or began on 3114 BC ? not really. The years 3114 BC and 2012 were the years where Mayans had to remove their old calenders and get a new calender. Just as we change our calenders on January 1st. The only difference is Mayan calender was so huge and one calender was enough for massive number of generations (Calender making would not have been a prosperous business in Mayan culture). They may have further extend their calender if they had more space and time to write the calender.

Although this 19th January 2038 does not physically end the world, many problems will arise in digital systems. Almost all the systems now been used would not be able to perform date calculations. The day will be reset to Friday 13th December 1901 after 2038 causing many problems. The solution is to increase the number of bits used to represent a date in digital systems. But this will introduce backward compatible problems with current software architectures. So still a universal solution have not been found. But probably in the near future people with come up with many plausible solutions and there is no need to fear about the end of the world, unless we dig our own grave due to wars and environment pollution.
http://en.wikipedia.org/wiki/Year_2038_problem