I have a good friend who is a Christian and usually talks about the doomsday as described in the Bible, when according to her everyone who have died will come back to life to face God's judgment (Those who really have read the Bible, please forgive me for any mistakes here).
I do tend to believe that there is an end to our time, just like there is a start (possibly out of nothing). That end may be explainable by a singularity in the development of human civilization. If our development can be measured by a monotonically increasing function with time being the independent variable and the level of develop the dependent, then if there is a vertical asymptotic limit line lying somewhere in the future (which can possibly be Year 2012), we will one day realize, in the final seconds of our time scale, that we have utilized all forms of resources in this universe and become "all-knowing", and since time is nothing but a form of energy, we will be able to take control of time as well. Time, as a dimension that constrains us in this positive direction (so that we cannot go back to the past) will lose its power and meaning, and literally we will have reached the end of time.
Alternatively, if human development follows some sort of exponential function, which is not asymptotic, if there is an upper bound to the level of development, then we will at some day "suddenly" reach a point that ends this universe we came to understand. Compared to the former scenario, this is less romantic, without the myriad of miracles that we will witness in the final seconds. How come there is this upper bound instead of any other is also difficult to reason out, rendering this conjecture not all that probable.
I picture in the doomsday, some individuals of human beings will transform into an existence close to God, and the remaining of our species may be wiped out from the Earth. A sad story. But it is nothing more than a million possibilities that our limited intelligence can come up with.