As wel all know, PayPal is an extremely popular system that allows money transfers over the Internet, serving as an alternative to traditional cheques and money orders. Now a subsidiary of eBay, PayPal had its own share of security problems, especially with phishing. Since these problems can happen to anyone, anytime, knowing how to protect yourself is the best thing to do, so PayPal published its own guide to "Safer Browsers", which can be read here.
To make a longer story short, they are talking about IE7's phishing filter most of the time, and have simply pushed aside Safari, without writing down a single word about it. Well, it may be that Safari still lacks some advanced security features found in IE7, Firefox or Opera, but some voices also claim that PayPal's heavy use of Extended Validation certificates may also be a problem, so Safari it's not that bad, after all.
In the end, it gets down to user's attention, because every time, before being detected, phishing sites grab a few victims for sure, and that's not because their browsers, or because PayPal's own problems, so no matter what browser you are using, feel free to look twice, think 3 times, and only then submit your valuable personal information!