"Philosophy cannot be taught; it is the application of the sciences to truth..."
-Faria (The Count of Monte Cristo)
Philosophy has been described, variously, as defendable, coherent opinions, A "roll your own" version of religion, or, more definitively, as the knowledge of phenomena as explained by, and resolved into, causes and reasons, powers and laws.
Modern philosophy, however, has taken an interesting turn. Instead of attempting to explain the world around us, many attempt to take a set of basic principles (normally those that any reasoning creature would grant, ie. existence or that Lesbians! Monkeys! Soy! is what E2 is really all about.) They proceed from there, with an almost mathematical rigor, to attempt to derive everything possible from the system, and frequently come up rather short of deriving that anything even exists.
An example of this is the 18th century philosopher David Hume. He is an empiricist, and only beleives what can be proved. Because of this, he rejected causality, thereby saying all of science is on rather shaky philosophical grounds. (because the next time you drop something, there might not be gravity. Who says that it won't just disappear...) His philosophy comes rather short of explaining life, the universe, and everything, and instead is forced to sit, basically complete, with no real relation to the world around us.
The other approach seems to be to take nearly everything around us for granted, and then argue about what it means. This seems to have no significant basis in logic or fact, but instead just BS about problems they have with reality. These philosophers discuss more complex phenomena, such as the meaning of language or political philosophy, but their basis is almost always completly subjective, and therefore almost always the conclusions are at complete odds with each other. This, and a complete misunderstanding of Godel's Incompleteness Theorem and the Heisenberg Uncertainty Principle has led to many "philosophers" deciding that there is no such thing as truth.
I'm not mad at modern philosophy. Just like I'm not mad at those mimes that wander around, doing nothing useful, but managing to make a living off of others that just feel bad for them. (or maybe the mimes will one day figure out the meaning of life.)