Sharp,

Substential precense test applies only if you are resident for a part of the year. For example, if you are in F1 from Jan to Sept and in H1 visa from October to December, you are a part year resident. In that case, substential presence test can be applied. You can wait until the first week of June to qualify for this to file the tax return so that you can file as a US resident. You have to worry about this if it happens before you are here for less then 5 yrs.

This thing is kind of tricky that is why I knowingly omitted from the conversation. After 5 years, you don't really have to worry about what visa you are at, you can file as a US resident. This is a right statement. Jonny is right in his posting. If you read through the publication 519, you will know it.