Honestly it has more to do with how much time I want to spend on the site, how much it returns, and whether or not I should spend my nights and weekends transferring it to another host.
The last time I backed up all the data from GAE it took 4 days to download all of it to a VPS. 4 days to download all of it. Migrating means 4 days of downtime, or alternatively some complex solution involving posting all new data to BOTH places while the migration takes place.
That takes time and energy, and quite frankly I'd rather see someone with the resources do it right instead of trying to hack it.
