Contribution import fails for all records with error "No matching Contact found"
The only change to the file CRM/Contribution/Import/Parser/Contribution.php between 4.6.0 and 4.6.6 is the addition at line 263 of:

$params['contact_type'] = 'Contribution';


Commenting this out seems to fix my problem.  My contribution imports are based on matching the individual contact by email address, so I'm guessing that this line broke things by forcing a lookup by contribution ID.

Should I file a bug report?