It's certainly slower, and more durable, than local disk for writes. For reads/stat()ing this is mitigated to a certain extent by optimistic caching in memcache

It's certainly slower, and more durable, than local disk for writes. For reads/stat()ing this is mitigated to a certain extent by optimistic caching in memcache. You also get the advantage, for asset pipelines, in that GCS can serve the generated file directly.