A question with a thousand answers, Kash.

From what I can tell, the biggest complaint regarding the SEO of an iframe is whether the frame is content that is at the same url or pulled in from another as well as whether the content in the iframe links back to the stuff outside of it or not.

For example, I've seen people try to take the WHOLE wordpress or blogger type blog and place it in the iframe as above, including all of its own internal navigation, which of course doesn't go back to the parent site, but gets you around within the blog.

I have two preferred methods for dealing with Blogs and Xara:

1. Create the blog (in wordpress.org, locally hosted in my case) external to the Xara site completely. Customize the wordpress template to look a lot like the rest of your site, copy the banner and other identifying elements to the wordpress template, and create links in the navigation area that point to the various pages on your regular site.

or

2. Create the wordpress.org based blog and strip the header, sidebar, and footer parts out of the php engine for the blog loop (which probably sounds harder than it is). Then iframe the main portion of the blog within a placeholder in the Xara site. The benefit here is that it's a little easier, the blog is ON your site and looks like it but you didn't have to rebuild a whole template to get it there. The downside to this is that the things like RSS and such will link directly to the wordpress innards - so people going back to your site via those feeds would get a mostly unstyled page rather than to the shell of your site that iframes the wordpress contents in. So your best bet here is to not have the RSS and such on that Blog - which is fine for updates from the site owner, but does kind of side step one of the useful technologies of Blogs - the social and autoupdate nature.

Another option to deal with option 2 is to create your own RSS feeds that point to the right page within your host site. There are some issues with this as well, and it certainly takes more active maintenance to keep up with.

Hope this adds something.