What are some likely differences between a test and a production environment?
Re: production environment
Sizing and location of files/queues/dbs. This may affect response time as well. Your test environment may run data across different lines for test/production. Size and breadth of test data vs. production data can also be an issue. In order to run tests more efficiently, overnight cycles may be abbreviated, or dates may be artifically changed, which may change "trigger" action. Test servers may be configured differently from production servers, with different failover and backup requirements.
If you're working on web app, it's really complex, since there's no way to tell what kind of software your clients may have running simultaneously on their machines.
A test environment tends to be smaller, more controlled, and pristine than a production environment, again, to ensure test efficiency. It also needs to be restorable; you don't normally restore your production environment unless you've had a catastrophe.
Thes are a few things I thought of immediately; I'm sure there are many more...