I understand the concept but haven't kept up with recent developments. As I see it, Ripple is only geared towards debt payment, it wouldn't help me much in assessing the safety of buying stuff from an anonymous seller. A WoT like bitcoin-otc does help a great deal in that department.
If you think ripple doesn't help you to safely buy stuff from an anonymous seller I think you haven't understood the concept.
You can pay with ripple. Ripple is a medium of exchange.
With ripple you could just use reputation as a currency.
For example, I give you 2 reputation points by paying you 2 units of currency I issue denominated in reputation points (or IOU 2 reputation points) and your web of trust can be represented within a ripple network.
Related links...
Reputation as currencies:
http://metacurrency.org/http://www.webisteme.com/blog/?p=308Ripple (and therefore a WoT too) inside a chain:
https://bitcointalk.org/index.php?topic=37505.0