I'd avoid all possible business with them.
They behave and operate as a bank, but since they're not, they are under zero rules and regulations that 'real' banks have to follow.
This means they can get away with murder. Google around the subject, and you'll find many, many cases of people having thousands of dollars in their account, then it getting frozen for some random reaon, and them being unable to take out their money.
Unfortunately, it's owned by eBay, and so eBay encourages you to use it (a lot). Since eBay is the main horse in town when it comes to online auctions, this means that you're sometimes pretty much forced to use it.
If you do use PayPal, remember to take out any money you have in your 'account' and move it straight to your real bank account immediately.