If someone does decide to match you, they should also announce and retroactively ask someone to match them, and so on...
The 'forward' way to do this, "I will donate $150 if someone else commits to this statement.", may or may not be better.
I see no reason to disagree with you. (By the way, the other time I did this was non-backwards.)
A note for potential matchers: if you match this donation, you'll make me more likely to donate in the future. (I'll be like, "Not only would I be helping out, but I could probably get someone to match this donation as well. ") I was relying on this being obvious.
I just donated $150 to the Singularity Institute. Would anyone be willing to match my donation (as in, donate at least $150 and tell me you did so)? A first-time donor would be ideal, but anyone would make me happy.