On May 22nd at 3:00 AM PDT for NA, 5:00 GMT+1 for EUW, and 3:00 GMT+2 for EUNE, servers will go down in preparation for the upcoming patch.
Here's 2changz with the NA version of the maintenance announcement:
"On 05/22/2014, starting at 01:30 PDT, ranked queues will be disabled in preparation for patch 4.8. At 03:00 PDT, the servers will be shut down and all games currently in progress will end in a draw and stats will not be recorded. We estimate the battlegrounds will be unavailable for 6 hours."Here's a collection of the patch 4.8 maintenance threads for each server:
I'll keep you updated as more information on what the patch contains and patch notes become available. While the latest PBE content is usually a good indicator of what's to come, please remember that it is tentative and not everything may make it to live.