WP7 Marketplace FAQ: Do my free app submissions reset every year?
Yup, you get 5 free submission credits a year, so every year you could potentially submit another 5 free applications to the marketplace (not to mention the unlimited free updates to existing free applications).
Can I see how many submission credits I have left?
Not at this point, though I hope to see this soon. For now, if you can't remember where you're up to, submit a support request and the team will get back to you asap (usually within 24 hours) with an answer.
Is your head spinning with all the free yet?