Is paypal good for a savings account? Are there any dangers in keeping a high balance with paypal?

Paypal's moneymarket interest rate is around 5% right now, which is competitive, if not just better than, local savings and cd rates. My temptation is to use paypal as a place to store some savings, like up to $8000 over the next year or so. I'm curious if others are doing the same? Are there any reasons not to? It's still relatively liquid, right?