WordPress MU

I have a blog network running on MU with Donncha's Domain Mapping Plugin. It's not an open network, all of the blogs are mine, I just use MU because it's easier to manage all my writers and upgrades. There's one thing that is concerning me and another that is puzzling me.

Concern: when you load one of the blogs for example blog1.com in the browsers status bar it says blog1.mainurl.com while it's loading. I'm not completely clear on the implications of this but I'd prefer the MU architecture to never show through to the front end.

Question: in the back end under the blog settings (Blog info (wp_blogs)) there are several fields where the full url are displayed:

Siteurl: http://blog1.mainsite.com
Home: http://blog1.mainsite.com
Fileupload Url: http://blog1.mainsite.com/files (although theres another field "Upload Path" that says "wp-content/blogs.dir/8/files")

Should I change all those fields that say http://blog1.mainsite.com to say http://blog1.com ? I understand that Donncha's plugin filters and rewrites these values as they are called but if I want to fully mask the underlying architecture of the site, should these values be changed?

There is a (paid) domain mapping plugin that does exactly that.

Since all the blogs & domains are your, just take one for now on the Edit Blogs page and change the values to the new domain instead of the sub. It *should* still work just fine.

Oh boy, I tried changing one of them and now none of my permalinks work anymore. I put everything back the way it was and they still don't work!

Ok, it's fixed now and I don't know why. It seems that there was a lag but I don't have any caching running.