I’m a little late to this party since others have mentioned this several hours ago, but you can sign up for instant Gold status in the Hilton HHonors program just by entering any Visa Signature credit card number.
The status will last through August 31, and three Hilton stays by August 31 will extend status through March 2013. Gold status gets some modest upgrades with Hilton (even Diamond doesn’t include suites as part of the terms and conditions of the HHonors program) and it gets complimentary breakfast.
The offer is supposed to require a US-based Visa Signature, but there are reports of non-US cards working. The offer also specifies that the three stays to extend status must be paid for with a Visa Signature, though it’s unclear whether this will be enforced.
Current Gold and Diamond members can still sign up, and will receive 5000 HHonors points. (The page doesn’t say this prior to entering your information, after Gold and Diamond members sign up the site will acknowledge your current status and indicate that they’ll be giving you the 5000 point bonus.)
It does seem that the IT behind the offer is somewhat glitchy, it can take a few signup attempts to get this to work. Personally my sense of irony required me to enter my Hyatt Visa number rather than my United Visa number in order to sign up for the offer…