Forget to mention, it's unlimited downloads from 2am - 7am eastern every day. If you were throttled, it's discontinued between those hours. If I'm running bit torrent or doing a full website download, I'll schedule it to run during those hours. Any usage during that time doesn't count toward the daily limit.
I once heard the algorithm hughesnet uses for the cap/limit described like this: imagine a bucket of water with a small steady stream of water filling it from the top. When you download, you're emptying the bucket from the bottom. You can get a big flow out for a little while, but once the bucket (the 550mb) is empty, you're only able to go as fast as the small steady stream that's refilling it.