We've recently seen an issue where the ColdFusion 9 installation program on 64-bit Linux will not accept (will reject) valid ColdFusion 9 Standard license keys (a.k.a serial numbers). You may see the following fail (failure) message:
The serial number that you entered is invalid
The workaround for this issue is to install ColdFusion 9 as Trial--that is, do not enter the license key (a.k.a. serial number) during installation--and then enter the license key (a.k.a serial number) via the ColdFusion Administrator after the installation has completed.
This issue only applies to ColdFusion 9 Standard license keys (a.k.a serial numbers); we have not seen any issue with the ColdFusion 9 installation program on 64-bit Linux accepting valid ColdFusion 9 Enterprise license keys (a.k.a. serial numbers).
2009-12-02 UPDATE: There is now an Adobe TechNote for this issue.