Occasionally IntelliJ pops up the update dialog asking me to update to the latest versoin:

Usually I'll just click Remind Me Later and continue on my way, but this time I clicked the Ignore This Update button. Now anytime I go to check for updates, the event log states:

Update Info
You already have the latest version of IntelliJ IDEA installed.
To configure automatic update settings, see the Updates dialog of your IDE settings

After some digging, I found a post from Dmitry Jemerov on the Jet Brains support forum which stated:

In the current build, you need to edit the settings manually (under in other.xml).

That's good info, unfortunately it doesn't provide any information on the location of other.xml. After a quick check of the normal locations, I was able to find other.xml at %userprofile%\.IdeaIC12\config\options.

Once in that file you need to search for myIgnoredBuildNumbers and simply clear out the content, so it looks like this:

#!xml
<option name="myIgnoredBuildNumbers">
</option>

Now IntelliJ will notify you of the update again and you can keep on telling it to remind you later.