It is a little odd that Google has labeled 4.0.3 as the baseline version of ICS, but the Nexus S and Galaxy Nexus are only getting 4.0.2 starting today, but it would seem likely that another update wouldn't be too far behind these. Still, if you have a GSM Galaxy Nexus either outside of the US, or as a US importer who just couldn't wait, you may see this update pop up sometime soon. Early reports had users in the UK and New York seeing the update first, but it's sure to spread.
Android 4.0.2 is a pretty small update, just under 9 MB, and is cryptically labeled as "bug fixes". The bigger changes are slated for 4.0.3. If you're adventurous, xda has a walkthrough in how to manually update, but it's unclear how safe that is at this point.