Will give you my own mini-review, even though you didn't ask for it...

Pros:

Price - cheapest worldwide card. Excellent rate of $.95 outbound and
$.35 inbound EVERYWHERE. No zones with varying prices, no time of day
restrictions- only real "flat rate" worldwide card out there. Also
checking your balance and calls to CS are free of charge.

Performance - On a recent trip to Italy/France/Spain/Austria/Poland,
callbacks worked about 75% of the time, first attempt. This is pretty
damn good. If callbacks are not coming through, switch to another
cellular provider in the area.

Web Access - Can check account balance and divert status online (as
well as on the handset).

Cons:

Customer Service - non-existent and generally unhelpful. Most of the
time, calls to CS result in the message "the phone you're calling may
be switched off". Took me three days to get hold of someone once.

Purchasing issues - If you purchase the card and recharges directly
from Hop Mobile (the most inexpensive way), they only accept
Mastercard. No Visa, no checks or money orders, none of that stuff. If
you purchase from a reseller (Telestial et al.), they are more
flexible with payment methods, but your prices are much higher.
Understandable, but inconvenient nonetheless...

Weak Coverage - No Central / South American coverage. No Brazil, no
Peru, no Venezuela, no Paraguay, no Mexico!!  African coverage is
good. Their website promises more countries to be added, but none have
been recently.

Services - no voice mail and no data. SMS supposedly works if your
handset supports SIM Toolkit (only a handful do). Also, no option to
send/receive caller number ID (all calls are "unknown"). United Mobile
offers this for a fee.