For those who don't want to read about an arcane bit of commercial paper law, please stop reading now.
Much as I respect you Eric, I direct your attention to the myriad of "checks" being sent out by AT&T and MCI, to name a few offenders. These bear the legend: "endorsement of this check constitutes your acceptance of <foo> as your long distance carrier."
From West's Nutshell handbook on _Commercial Paper_, p 55:
"[...] an instrument is not negotiable unless it contains an unconditional promise or order. [UCC] 3-104(1)(b). See 3-105. That is, the obligation must be expressed in terms which are absolute and not subject to contingencies, provisos, qualifications, or reservations which may impair the obligation to pay. It must be a 'courier without luggage.' Overton v. Tyler, 3 Pa. 346,347 (1846)." If a check is not negotiable, that does not mean that the order on it is invalid; it means that the rights of third and later parties to collect on the order are precariously held. This might not impede the money getting transferred, though. The thing about the LD company checks is that their writing doesn't seem to be a condition on the order to pay. After all, you don't have to indorse a check in order to get the money from it; you can always take it to the bank it was drawn on directly. The condition on these checks seems to be a condition upon your indorsement of the check; conditions on indorsements do not affect negotiability.
Weasels.
I agree. Eric