Review: http://weblogs.about.com/cs/blogsoftware/gr/wordpress.htm
Pros:
- This is the exact same as the installed version, minus the hassle of installation, upgrades, machine maintenance, etc.
- Totally up to date with all the latest widgets - really an incredibly complete solution.
- Active development and support in the forums.
Cons:
- I believe at the moment you have to use a wp.com domain name, you can't use an existing one (but you could with a clever frameset).
- Customization is limited to existing templates.
Free!
Example: