Facebook has put word out to developers that it's going to be upgrading the maximum size that it displays pictures at over the next few weeks. Photos will be going from 604 pixels wide to 720 pixels - nearly a 20% increase.
That means that those terrible pictures of you singing "Total Eclipse of the Heart" last Friday are going to be even larger, your bloodshot eyes more visible, and the red wine stains on your blouse even more evident. Sorry. Photographers will be pleased though - image size is one of the biggest complaints from users that upload a lot of pictures to the site.
Facebook hasn't stated it outright, but it's likely that old pictures already up on the site will be bumped up to the new size if they were uploaded large enough already - the company keeps the original files on a server and can generate any size they like at any time.
In other image size changes on the site, profile pictures will be getting a slight shrinkage - down to 180 x 540 from 200 x 600. If you're the developer of a Facebook application that accesses a user's pictures, you might want to take a look at your app and make sure that the changes won't break anything.