My experience with PayPal has been that they are fine as long as everything runs smoothly and you don't have any special needs or hit any glitches. The automated aspect of their system is great. The problem comes if you hit a situation that requires the intervention of a live human being. Then you can expect a descent into total hell.
Fortunately this has only happened to me once since I signed up with them, but it was pretty bad. Basically, a client tried to transfer me the initial deposit for her web site, and in response they froze both her account and mine indefinitely, with no explanation, for alleged "violations of PayPal's terms of service". Both my client and I wrote to them over and over trying to get an explanation, and all we got was form letters restating the same thing, without ever saying what part of the terms of service we were supposed to have violated.
Eventually I posted about the problem on a web design mailing list, someone pointed me to a discussion forum on an auction sellers' site that had a forum specifically for PayPal problems, which was monitored regularly by a sort of PayPal ombudsman/troubleshooter who seemed to have a fairly good track record. So I wrote to him directly and got it resolved with an apology inside of 24 hours!
Apparently they had suspected the transaction of being fraudulent because of the fact that my client had only just signed up with them and had a Hotmail address. So since then I've suggested that people use a real domain or ISP address when signing up rather than a webmail address, and not transfer large amounts of money until you've already done a few small transactions to establish a history with them.
Anyway, the address of the person who sorted it out for me is damon@paypal.com in case anyone else is in need, though it was almost a year ago so I can't guarantee he's still there.
I do still use PayPal - I can't afford the security deposit for a merchant account, so it's the only way I can take credit card payments - but I'd be a little wary of depending on it as the sole support of a business.
Another option for remotely hosted e-com transactions for small businesses is Mal's E-Commerce (http://www.mals-e.com). I've set this up for one client and it was pretty straightforward, and they seem happy with it. Wouldn't use it for a large business or someone who was concerned with making a very professional impression though - it's obvious that it's remotely hosted and that says "cheap" to most people.
Lynna
Business: http://www.spidersilk.net
Personal: http://www.wildideas.net