Just last week I had my account 'restricted' which is their current term for what happens when a chargeback happens via Paypal. My bank (Natwest in the UK) put a stop on the Direct Debit authorisation due to several small amounts going out in one fortnight - Steam sales! - which their fraud team saw as fraudulent activity.
This meant over a week after I had downloaded and been playing the purchases on Steam I had a series of emails from Paypal saying disputes had been initiated by them and then an alert from Valve support came up on Steam as I logged in to inform me I'd had my account restricted and the purchases in question removed from my games list. I am still able to access over 250 other titles (I've been on Steam since 2005) in single or multiplayer but I can't purchase anything, trade anything or redeem codes like the recent Humble Bundle that came out.
I've cleared the problem with Paypal by re-authorising the Direct Debit with my bank and am waiting for the long slow response cycle between Paypal and Steam to complete so I can have full functionality returned to me.
Long story short - Paypal are dicks, don't use them unless you need them for ebay, they are the ones who authorised a payment to Valve and 'stole' the items from them essentially.