For months the Fedora developers have been planning to mount /tmp with tmpfs for putting the temporary directory in RAM/SWAP volatile memory as it will lead to less disk reads/writes, potentially save power / better the performance, not preserve temporary data across reboots, and other benefits.
Due to open bugs (e.g. 858265 and 873831), it was brought up to decide whether to disable this feature by default in Fedora 18 until all the migration bugs are worked out. However, it was determined at today's Fedora Engineering & Steering Committee to stick it out with this feature of having tmpfs be used by default.
The meeting minutes can be found on the devel mailing list. They also made a few other changes at today's meeting with regard to refining the feature process and moving the final change deadline up by one week.
After being challenged by numerous delays, Fedora 18 is expected to be released in early 2013 under the Spherical Cow codename.