OK, let's assume you can try 1 billion (10^9) keys per second. Now add numbers to your keyspace (remember, no special characters or capital letters yet!), and make your password 12 characters instead of 8. Not much harder for you.
But now it takes 150 years to brute-force the keyspace.
I doubt anyone is going to devote 150 years of computer time to someone going through customs.
First you can use a dictionary - then munch it (with Jack or something) to create a large dictionary within the keyspace. It's surprising how much that covers.
Then you can parallel the process; I know a few commercial companies (ourselves included) with a large computer capacity for these purposes. I'd be surprised if the govt. didn't have some form of similar access.
If you can reduce the search space by a factor of 1,000 and run your cracker on 1,000 machines it makes a dramatic difference.