[Serious] Generally speaking, is philosophy a worthwhile subject of study?

[Belacqua]

Philosophy is wonderful to discuss with friends over drinks (Symposium, anyone?) but is rather useless as a source of knowledge.

[...]

Sometimes, you don't need to do anything but show up to the bar in order to philosophize. But other times, you need to do six and a half hours of reading and try really hard to understand something before the discussion can transpire. Treating the whole of philosophy like some quaint "night out for drinks" is inaccurate.

At the beginning of Plato's Symposium they decide they're not going to drink any alcohol that night. 

People should read the books they think they know about.