I've linked WePay to my checking account (50 cents per transaction) so settling with my roommates takes less than a minute, once a month, and the convenience of not having to lick an envelope and remember to mail it is worth the extra 6 cents (as opposed to paying for a stamp).
One of the big differences I see here is that billshare doesn't handle the money! WePay actually handles accepting the payment, and distributing the funds. You can then get a check, or better in many cases, spend it using a WePay debit card!
All it really does is expense tracking - you can post bills, and find out who owes who how much. There are also some semi-vanity features like stats on where the group is spending its money.
I think billshare is good enough when you know the people in the group and can trust them to repay you when necessary. Otherwise WePay is probably the way to go.
My first company, http://www.hoodeasy.com, has worked pretty well using this model. We're a middle-man between clothing suppliers and groups of students. Our selling point is the ease of group-ordering. Our margins are a lot higher than around 3% gross but we have a very niche focus. Another startup in the UK, http://www.wigadoo.com, tried to do lead-gen for group-bookings of holidays and really struggled. They folded around August 09. Group ordering is definitely an interesting space. Sites like http://www.groupon.com have the model just perfect because they focus on facilitating the mass-sale of high-margin products where the fixed costs of those business are quite high. I wish WePay all the best.
Effectively there was one a few weeks back leading up to Thanksgiving; these announcements may just be the tail end of those deals being finished up and having all of the legal stuff sorted out.
Me and my roommates use it and it has suited our needs fine for years