In version 4, RapidWeaver converted over to an open XML file format for saved files. The new "bundle" format should make developers and users alike happy as it opens the doors to allow third party developers to create applications that can interact with RapidWeaver files (which can now be done without developing RapidWeaver plug-ins).
In addition, RW 4 provides 4 additional themes, bringing the total number of themes up to 40 (wow, there's too many 4's in that sentence, eh?). In addition, you now have true, one-click publishing from within RapidWeaver 4: .Mac, FTP, and SFTP are built right into the application.
RapidWeaver 4 really shines in the user interface category. RW was revamped for this new version with a completely redesigned interface. Building on Apple's Mac OS X Leopard standards, RW 4 brings a whole new game changing application to the web design application category.
RapidWeaver just feels like a professionally designed application from the moment that you open the dmg file and drop the application into your Application's folder to the moment you upload your website to .Mac or your own server. In using RW 4 for a couple days, it performed seamlessly. Not only does RW have some new features, new interface, but you get the feeling that you are using a well designed piece of software -- RW 4 begs to be used regularly!
If you are looking for an alternative to iWeb that has more features, or want to step into the wonderful world of creating your own websites/webpages, then I would definitely recommend giving RapidWeaver 4 a try. Realmac Software allows you to try out RapidWeaver 4 for free. RW 4 is a free upgrade to users of RW 3.6 and higher; however, if you will require a new license, pricing starts at $59 for a single user license. You can find out more information about RapidWeaver 4 on the Realmac Software website.