I don't think there's any punishment for being a leech, go read their FAQ and Rules if you're worried. At most you'll get a pop-up saying you should contribute but it'll still let you download, maybe some people lock their uploads and only give permission to save them to contributors that ask, but that'd have to be done manually and it's retarded so I doubt many users do it.
At least be mindful of mass downloading. Do you really not have any legit CDs you could rip? Windows Media Player lets you do it very easily.