Are there advantages or disadvantages to using PayPal?

I have noticed that PayPal is an option more and more to use for paying for things online. I admit, when I haven't used a website to pay for something before I am glad to see the PayPal logo. I feel like it could just add a sort of "middleman" in paying for something. I have never had any problems with using PayPal for eBay. Thoughts? Experiences?