Been using PayPal for several years without any problems. Absolutely safe and secure - although beware bogus e-mails asking for details to be confirmed by clicking on a link. As with other financial institutions, PayPal will never e-mail such requests.
I've used it without problems. As mentioned above there fees can be high (always charged to seller), something like 20p + 3.4% which looks small but can add alot. They offer various forms of accounts, some that have no fees and others that do (if you wish to be able to recieve payments from a credit card).