Yeah I bought 4 for $20, and that gives me a secondary for each batch I make. That way when I rack onto the secondary I can start a couple new batches and when it's time to bottle I'm ready to rack the other batches to the secondary.
I use the 3 and 5 gallon plastic containers for drinking water (they sell them in Walmart back in the hardware section). The advantages over the traditional PET carboys is that they have molded in handles that make it easier on the back when moving, and they are certified not to absorb flavors (read chemicals, so no discoloring) or release molding agents (read chemicals) into the "water". Here's a picture of what I am writing about :
Bet you they are way cheaper than better bottles too!
I think as a primary they aren't a bad source if you are in a bind. I think for long aging I get nervous in plastic. Though it is probably unwarranted
Having a secondary (an empty one to rack into) is key. It sucks, but every year I have one 15 gallon demi-john empty floating around as a racking fermenter. However, it just makes life easier than racking into homer buckets, then cleaning demijohn, then back into demijohn.