USCIS has finally announced that the fee increase will be effective on July 30, 2007. If you've been planning to apply for citizenship, or have a green card ($370 for the I-90 Application to Replace Permanent Resident Card) or conditional green card ($545 for the I-751 Petition to Remove Conditions on Residence) that's going to expire, you should think about sending in your forms before the effective date.
Since this is an expansive raise, if you're planning to file anything with USCIS, consult with an attorney to find out whether you can avoid the new fees by seeing if you qualify to file at this time.
And if you've been thinking about naturalization... get started now! Not just because if you wait, you'll be paying $675 instead of $400, but because if an emergency arises in your home country, and you have to return for a lengthy period, you may find it difficult or impossible to return to the United States. It happens more often than you'd think.