If you bought a Nexus device so you could happily flash all manner of custom ROMs, today is a good day. MIUI has updated their codebase to include Jelly Bean for the 2.8.17 release, provided you have a GSM Nexus S, a Galaxy Nexus (in either GSM or Verizon's CDMA/LTE flavor) or a Nexus 7.
The ROM will have all the goodies you expect from MIUI, with the addition of things like Google Now, and that delicious butter that makes all the difference. On the surface, things will look a lot like the previous versions of MIUI. Like Samsung, or HTC, the folks at MIUI have a look, feel, and feature set they think is worth keeping. A whole lot of users agree.
No word on when to expect any newer versions for other devices, but you can be sure the team is hard at work, and much will depend on manufacturers providing the necessary hardware drivers and kernel bits. In the meantime, MIUI fans with Nexus devices can find all the details and download links at the source link.