It may not be the best choice for an infrequently used Web page or App because your "slice" sleeps if not used for a while and the JVM takes a while to start up.
This is true, but should be a minor concern--you can easily ping it every once in a while to keep it hot without using very many resources. You might even be able to use App Engine's built in cron jobs to do it from the instance itself (might need more often than once a minute though).
