I haven't used it but it's interesting.
pro: very low fees. A quarter.
con: who accepts their payments? Hardly anyone.

I signed on with PayPal when they were about this size. Nobody'd heard of it, they were giving new signups 10 bucks just to join. I've never had an issue with PP but sure don't like their fee structure.
Looks like Dwolla is growing. For now it appears that it might be worth testing if you have someone else with whom you frequently exchange money. Shopping online? Not so much.

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You're a daisy if you do.
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84 Euro 240D 4spd. 220.5k sold
04 Honda Element AWD
1985 F150 XLT 4x4, 351W with 270k miles, hay hauler
1997 Suzuki Sidekick 4x4
1993 Toyota 4wd Pickup 226K and counting