That's an interesting idea.  I wouldn't make the clients mine, though.  Not everyone has access to a reasonable mining rig.  Just have the clients pay BTC for premium bandwidth.  For instance, offer to pay 0.001BTC per MB of transit.  That's highly profitable for the relays - it's a 100x markup over premium internet transit.  And it'd be a reasonable price for many users who want to go fast.

The two problems I see: 1, you'd have to prepay for your bandwidth, though that's not so bad when you can do very small microtransactions with BTC;  2, if you get your BTC from a non-anonymous source it defeats the purpose of TOR.  Clients who care could mine their own; most won't care since they're not worried about a threat strong enough to trace the coins back.

My gut reaction was: no way is this going to happen, mainly because people who mine usually want the Bitcoins for themselves. On further reflection, I think this isn't quite impossible to get working - maybe in the TOR userbase there are people who'd be willing to part with some GPU cycles to support the system, even if they wouldn't be interested in mining as such. I think you'd have to make it voluntary, though, with the TOR installer / executable asking the user if they're willing to mine, and my feeling is people tend to say no when they're asked to do something extra.

In other words, there may well be a bunch of people who'd go for this, but whether it's big enough to justify the effort, I don't know. The biggest problem is, you'd probably have to get it included into the TOR client, which is likely to be an uphill battle as it would probably seem somewhat tangential to their actual focus.

4) Paxum will not accept a scanned image above 4 MB in size for identity verification, but states that images must be "high quality" and rejects faxed images.  It took me several tries to come up with an image that was of a size it would accept and also a quality it would accept.  This is *really* annoying.

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Are you sure, you entered your order without typo?

I've got only good experience with Bitmarket so far, selling this weekend last time.

And it happend already twice to me, that my counterpart asked for cancellation because of a typo on his side.

Perhaps you should write an email describing your problem to BitMarket staff.
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^^ this

What settings did you use on the trade? i.e any stop/limit, market, etc etc?