This is more likely to happen in SQL 2012 where they have changed caching for IDENTITY, so numbers may skip more abruptly when SQL Server is restarted. But there are lots of other possible reasons. For instance, someone runs a mass-insert of 1000 rows which fails or is rolled back.

What you should do about it? Nothing, of course. When you chose to use IDENTITY, you also chose to accept gaps, and whether these gaps are 1, 2,3 or 1000 is immaterial.