Two days from now Microsoft will remove the Windows 7 Release Candidate from their website. If you want to test out Windows 7 for free, then you will need to download this before the 20th August, 2009.
Windows 7 users who are currently on the release candidate will not have to worry until March 1, 2010 and June 1, 2010 when bi-hourly shutdowns and license expiration's will begin.
Alternatively, if you want to get your hands on the final release now, Windows 7 RTM is now available to Technet Plus and MSDN subscribers. You can also get a copy of Windows 7 through your institute using MSDNAA, or, if you participated in the private beta, you will receive a free copy of Windows 7 Ultimate.
Windows 7 is due for general availability on the 22nd October, 2009.