The most beloved Android modder, Cyanogen, has released the CM 7 RC4 that is said the be the most stable version of CyanogenMod 7 till date. This makes it compulsory for you to update yourself from the previous version. Also, the developer goes on to say that a couple of bugs like GPS and Nexus One Call Audio ones haven’t been fully fixed, but since this is more stable, you may want to update.
The most notable new fixes are on the tablet side of devices. The Nook Color, for example, now has working hardware acceleration. Because of these fixes, many of them are receiving their first RC. There was also a big fix from AOSP for EGL issues, which is why all devices bumped to RC4 from RC3.
Hit up the ROM Manager to download RC4 or CyanogenMod Forums in case you prefer manual downloads.