Hot on the heels of the just-released Android 5.0 or Lollipop, Android 5.1 promises to fix a few things. One of them is the memory leak in the Nexus line. This leak will consume all available RAM causing the launcher to crash. A sign of this is when the user sees the launcher redrawing when pressing the home button. Sometimes foreground apps will crash due to the lack of RAM.
Other nice stuff includes screen pinning, dual sim etc. See link below for more details.
Before attempting to flash Android 5.1, it might be a good idea to check your recovery manager. If you are coming from KitKat or older, it might be a good idea to upgrade. TWRP version 2.8 or higher use the new block name addressing scheme. See the quote from TWRP website.
Be VERY careful here. The older TWRP 2.8.3 and down used hard coded blk numbers for flashing and mounting. IF you are using an older version of TWRP please upgrade immediately. The blks for system/cache/data have ALL changed. IF you aren’t on the latest TWRP you risk flashing the wrong thing to the wrong partition on your phone! CWM has used blk names for a while now so this really only affects users who have not updated TWRP.
Messing up your partitions will give you a very bad day.
Update 17 Apr
I flashed CyanogenMod’s version of Lollipop, CM12.1 on 14 Apr. It has been three days. So far it looks and feels good. Screen response and refresh are much snappier.