I've been playing with Google Sites recently and found it to be a really nice site building tool, or at least a nice way to rapidly prototype a site.  Site architects are constrained to the toolsets provided; however, you can harness the power of Google's Gadgets as well as other Google Apps that integrate with Google Sites.

With relatively little effort I was able to create a personal site, salsafest.lunchsummit.com, using Google Sites.  In just a few hours I had familiarized myself enough with the tool to create a decent site framework.  Now, this site is not going to win any awards, but it was perfect for sharing with friends.

Some of the limitations and shortcomings I encountered include the following:

• No Google AdSense support.
• No scripting - there is no way to embed JavaScript into a page.
• Limited SEO control - there is limited control over page titles, but I did not find way to control keywords or descriptions.
• No CSS control - while you can edit your site's "theme," it only allows limited control of predefined items on the page.  There is no way to have or edit a custom CSS file.
• Quirky controls - some of the controls I worked with wouldn't always behave as expected.

Here are some of the features that proved useful:

• Custom site domain - it is a simple and straightforward process for serving your site from a personalized subdomain.
  
• Custom page name - there is full control over page names which can help boost SEO
• Automatic sitemaps - Google Sites automatically generates a dynamic sitemap XML document for search engines as well as a user sitemap page.
• Analytics support - it is simple to add Google Analytics tracking to sites.
• Webmaster Tools - Google Webmaster Tools are also easily added to sites.
• Docs - Google Docs integrate with Google Sites as well, the Google Spreadsheet Forms are particularly useful for building things like contact forms.
• Calendar - it is easy to integrate calendars using Google Calendars.
• ACL - limited access level control is also available, other Google Apps users can be added to the site as viewers, contributors or owners.  Additionally the site can be private or public.
• Gadgets - there are a bunch of built-in official gadgets at hand that offer basic functionality such as adding text boxes, links, images, etc.  There are also gadgets that provide list capabilities with sorting, tables of contents, slideshows, etc.

All in all I would say Google Sites offers a lot of power and functionality for sites that don't need to have a ton of polish, not to mention the price is right (it's free).  If you're building a non-commercial or personal website then give Google Sites a look.  It shouldn't take a significant time investment to figure out whether or not it meets your needs.  I'll try to post updates on some of the individual components of Google Sites in the future.