Hey jmerry, I want to apologize for accusing you of having chosen a poor solution. 99 out of 100 times, when someone suggests the home-button solution, they are complaining about deep backstacks. You are referring to a more profound problem of metro UI design (one for which WP lacks a good solution, where we can't just blame devs for designing a poor UI). In my defense though, you didn't initially mention what problem you were trying to solve, which is 'kinda' required info for posts like yours.
Anyway, I still don't think a home-button is an ideal solution, but for some scenarios and for some apps, it might be the only solution. I agree. I just feel that in addition to the guideline issue already mentioned, a home-button just doesn't feel metro like, as metro is intended to be free of navigational chrome. If a home-button can be avoided, it should be, which is why I don't think it makes sense as a general recommendation. An alternative solution would be to ensure an apps backstack is never more than one level deep... none of the issues mentioned so far exist in such apps. Other approaches also exist, but I can't think of one that would work in any and all scenarios like a home-button would.