By default, domains are placed on a regular release schedule and to move to a fast track whereby new features are introduced you'll have to make a configuration change from within your domain settings. Only administrators can do this. If you have a "Manage this domain" link at the top of your Gmail inbox, you are able to do this.
From your main Google Apps domain control panel, go ahead and select the Domain Settings tab at the top.
In this main Domain settings window, scroll down and you'll see an area that allows you to change release tracks and a few other granular settings. It's under the following section.
So let's go over the settings under this heading. The first one that you will see is the ability to automatically add new services as they come along. This allows for features to simply be added as opposed to scheduling releases.
The next one that you will see is scheduled releases. The way that this works is that Google will release features on this track Tuesdays only, at least one week after the feature was released to the rapid releases. This will give you time to talk to and possible prepare your users for any changes.
You also have the ability to change the way that the control panel looks through a few settings at the bottom of this section. If you set your configuration to next generation you will see some different things that are available ahead of time from the current version. Just remember that this feature is for US-based domains only.
Keep in mind that all of these settings are covered by all of your domains, and that for the most part the way that you configure this is really going to be based on how comfortable your customers are with Google Apps and quickly changing features. Also, you can always click on the "Learn more" link beside each of these configurations if you need more clarification on what specifically a particular setting may mean.
Which settings do you prefer to use when it comes to Google Apps feature releases?