There is a lot of talk in various forums that I follow about Maps API quota limits.
To summarize: there is a limit of 2500 requests per day per requesting IP (see: http://code.google.com/apis/maps/faq.html) , if your application issues those requests from any server you can reach this limit quite fast. The situation is much worst if your application is based in GAE then it has to share those quotas with any other application in GAE that happens to use the same API since all those applications are served from a limited number of google IP's making the API useless.
So far so bad except ... there is a solution, delegate the job to the client using JSON & JS. This way :
a) quotas are calculated against your user's IP and more probably than not he will never exceed those.
b) you offload some workload from your server.
c) save some bandwidth.
Practically I can't see a scenario where we can't use client side, since whatever we do we have to use the results only in connection with a Google map according to Maps TOS para 10.12 (unless of course you opt for the premier edition).