Finally, AppEngine team got us the best gift of all for this holidays. AppEngine 1.4.0, Always-On Instances and more. And Just $9 a month buys you 3 instances that can stay alive – even on low or no traffic. Those sites you want to host on spring, or even grails – which left you worried about darn bad startup times – You can host now with AppEngine worry free.
Google lifted/increased a few limits on different APIs to somewhat gracious levels. These may not be significant for most apps, but will definitely free your mind of concern