No contract denominated in Bitcoin is legally enforceable, because Bitcoin is not legal tender. So a salary contract in Bitcoin is merely a gentlemen's agreement: a good idea only if the employer is completely trustworthy (whatever you decide that to mean.)
..and that's different from getting a cheque how!?
It isn't.
Here's the thing about this discussion. It may work on a small scale, but right now the easy to access exchanged (markets) would make a very bad experience if some large payroll company started doing this on the last day of every month. . . there would be an immediate spike in the price due to them buying up supplies of btc and the employees would lose out on the deal because those close to the start of the list would get more btc and the ones near the next would be near the end of the micro bubble and get less.
Then once the price settles, employee #1 would have 10 btc, and employee #20000 would have less (maybe 9 or
or less depending on how big the payroll company was. In any event, the farther down the list the less number of btc the employee would end up with... and would effectively be absorbing the instability caused by the payroll company in the first place.
The alternatives to this are limited, but doable:
1. payroll company accumulates bitcoins slowly over time - then pays employees with them on 'pay day' --- here the payroll company exposes itself to risk re:bitcoin exchange rate changes between purchase of bitcoin and payment to employees.
2. payroll company load balances paydays over the course of a month between everyone it pays (your payday is the 1st, mine is the 2nd, his is the 3rd, etc) to mitigate the 'payday spike' on the exchanges. in this scenario, most of the risk is given to the employee rather than the company.
3. payday goes away and each employee is paid each day for his work that day in btc - this would mitigate the risk of the payroll company because they'd be holding btc only long enough to send it to the employee, and avoid exchanges being 'spiked' in the way I've described, but it would make it even harder on the employee because getting such micro payments exposes him to even more market rate issues since now he's forced to hold enough on an exchange or wallet somewhere before he can feasibly 'cash it out'
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of course all these go out the window if you were able to purchase all of your needs with bitcoin.
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personally, I would probably favor a job that paid me min wage + some other amount in btc. But that would be purely for tax evasion purposes.