Is buying and selling bitcoin in large volumes possible, or wise? I'm asking because I think it could be a decent investment, but on clarkmoody the volumes aren't very large.

Which could mean that bitcoin is only useful in small volumes, and that larger transactions (i.e. $ 5000 - $ 10000) will have to much of an influence on the price to be considered a wise investment (i.e.: you wouldn't be able to buy/sell everything at once without the price dramatically rising/falling). Any ideas/suggestions from the experts?
It is possible. You can go to Mtgox if you like, but of course you can make an offer in BITCOIN-OTC, "outside the market". If someone agrees your offer, this trade would't impact on Mtgox and similar markets.

It may be wise. You only need to be careful with people you agree to trade, using the "trust database" to see people's reputation, so you decrease the probability of getting ripped.