I don't see why fixed Mhash/s bonds get so much shit. You get dividends on a regular basis. You get the choice of what to do with your dividends. If you don't realize that you need to reinvest, just as miners have to reinvest, to stay competitive, you're going to make less and less each difficulty adjustment.

The bonds themselves might be worth less by the time you wish to sell, but the dividends you've received over time (and hopefully reinvested in something) need to go in the calculation of how much value has been created/lost.