In the example where he shows that the PayPal logo requires a bit of microcopy to explain you don't need a PayPal account to purchase, might it be cleaner to just feature the PayPal logo alongside the other credit card icons? The other example, where he specifies the billing address - well, I can't really think of a better way.
While I use it from time to time myself, my gut feeling is that if you find yourself needing microcopy, you might be missing something.
I refer back to this Nielsen Alertbox from 2005 http://www.useit.com/alertbox/forms.html from time to time. Basically, Nielsen thinks that "help" items are fine, as long as they're on the same page, in the same context, and your form is as short as possible.
I think some of the examples he gives at the end of the article are good in winning confidence, such as "we hate spam as much as you do" and "you can unsubscribe at any time". These things are hard to communicate through interface alone.
As for the Paypal thing, I hear what you're saying, but I think the microcopy should stay. It does no harm, fits just fine into the interface, and if it sways even one person who blanched when they saw the Paypal logo (next to the credit cards or otherwise), it was worth it.
While I use it from time to time myself, my gut feeling is that if you find yourself needing microcopy, you might be missing something.
I refer back to this Nielsen Alertbox from 2005 http://www.useit.com/alertbox/forms.html from time to time. Basically, Nielsen thinks that "help" items are fine, as long as they're on the same page, in the same context, and your form is as short as possible.