If Gmail storage grows at a rate of about 0.33 MB per day and you use the space the same as before, is there a chance you'll run out of space? Use this simple calculator to find out (type the date in this format: Month/Day/Year).
Update (October 2007): Gmail increased the rate of growth, so if you use Gmail for a long time or you didn't use too much storage, it's likely you'll see the answer "never".