This will be a long post. Since we are all human (probably), please do nit-pick my post if you notice glaring errors or the intrusion of opinion over fact:
I don't have much to offer to the discussion by way of physics or geology for this discussion (my background is in cognitive psychology), beyond those same perspectives regarding science in general, as offered by bengland above. There is a very specific problem with most debates in which the term "pseudo-science" is used, and often it seems to be an emotional one:
The term pseudo-science is defined perfectly, in my opinion, by Bengland's first post. "Thought that uses the language of science but not the method." This is generally how the term is used by the accusors (i.e. those taking the counter-view). The same term tends to be interpreded by the accused, however, as an insult (e.g. pseudo-science = "you're wrong" or "you're crazy"). It is most certainly not intended as an insult. Pseudo-science has a definition, and certain schools of thought fit that definition. Nothing more, nothing less. (http://en.wikipedia.org/wiki/Pseudoscience
In my earlier days studying philosophy, there seemed to be a distinction between true scientific thought and valid philosophical thought which is worth repeating here: Philosophical debates often value what is "possible" (i.e. all hypothetical scenarios are technically equal, as long as they have not been proven false), while most scientific debates value what is "probable" (i.e. the best argument is that which explains the most data). This audience probably does not need a primer on the difference between a scientific theory and a colloquial theory, so let's stick to the previous point.
The term pseudo-science is often applied to certain ideas (e.g. young earth, intelligent design, etc.) because they either are not established according to the regulations of scientific theories, or simply not supported by empirical data. This does not mean that the ideas are "false," any more than it means that the accepted scientific theories are "true," but simply that they fail certain tests of scientific rigor, and do not adequately explain what is observable about the world. In the scientific community, the "young earth" view is probably discarded for these reasons. The goal is to explain as much of the world as possible while assuming as little as possible to fill in the gaps, and if a viewpoint must posit additional assumptions to account for evidence that it contradicts, then the burden of proof is on those researchers to show that those assumptions are valid. Nearly every scientific field (as far as I can tell) follows this pattern.
I will give an example of a stance in psychology that is generally viewed as pseudoscience, but has still served a valuable purpose in the scientific community. J.J. Gibson, a researcher in the sixties, was pretty much fed up with the behaviorists, researchers who essentially viewed the brain as a computer that took the world as input and pooped out the output. To those researchers, the world had no influence on the processes of the brain aside from to-be-crunched numbers, and the brain was uninfluenced by its environment. Gibson proposed a revolutionary theory: the environment and the brain worked together to solve problems via "affordances," definite properties of the world that vary according to experience. Thus, it was not necessary for the brain to calculate the relative motion of objects in the periphery to determine its speed, but instead speed was a result of learned contingencies between "what you see now" and "how things look when they're moving fast." In his opinion, no internal computations were necessary, only the matching of the current world-view to learned contingencies.
Was he right? Well, yes and no. In the years since his research, fMRI data and ERP data have shown that we do in fact perform many computations on the visual world. On the other hand, ignoring the influence of the environment on perception is no longer generally accepted in the psychological community (indeed, this shift in focus has led to many sub-fields, and new understanding of phenomena such as change blindness and optical illusions [which are both SO cool, we should have a thread about it]). Thus, proponents of Gibsons original view today would be viewed as following a pseudoscience, since overwhelming evidence contradicts the strong form of that argument, but the view itself was extremely valuable to science as a whole.
To sum up for those who didn't really want to read a long post:
1a) Pseudoscience is a real word for a real category of ideas. It is not an insult.
1b) There is, and should be, a difference between what is possible and what is likely (given replicated and converging evidence)
2) Views that may have originally been classified as 'science' may, due to overwhelming evidence against them, be considered pseudoscience if pursued without adequately explaining the contradictory evidence.
3) The goal of any researcher should be to explain as much of the world as possible with the fewest unexplained assumptions about the world.
Finally, since the internet is a crass and biased place, I highly recommend this wikipedia entry on the age of the earth:
Interestingly enough, for you trivia buffs (and i'm including this because i found it neat, not to prove any point), eastern religions apparently plop the earth down at between tens of millions or billions of years, while western religions have, as we know, been much more conservative.