WordPress MU

Yes It's been discussed before.

But what are your thoughts on a mu sitemap? I've had experience with regular sitemaps for Wordpress and they all slow down and put much load on the WPSU sites I've used them on.

Is a sitemap needed? Any alternatives ?

IMHO, they're not really needed and cause an unjust load on an MU site.

I would have thought that with the arrival of tags (and global tag plugins) that sitemaps on blogs would really have no purpose because if the page can only be found by a search engine using a site map it's probably a "lost" page

So do global tags will help search engines as much as a sitemap does?

The only up side I have ever seen to them is if there are certain pages Google is ignoring for no known reason.

Otherwise, I've found MU all by itself is more than enough.

I only install it is the site owner insists on it because of the mountains of blog posts out there saying you need it (with not much backup).

Agreed. Sitemap can produce a huge siteload for very little gained. If a page is worth indexing, spiders will find it on there own.