A major issue with moving between systems is how to take the data with you. This is why upgrading from Elgg 0.9 to 1.6 is such a bear — the data formats are totally different and there is no officially supported data migration path.
Yesterday I finally set up a test WPMU system on my sandbox server. Once I had sussed out Apache vhost entry, CNAME, and DNS issues (it helps to do a DNS refresh!) I had blogs.sergius.earlham.edu working. The first thing of course was to find free themes which I did and now there are hundreds there. The next thing was to see whether data from this blog could be imported. I used the WP.COM export facility, downloaded the file and then uploaded it into blogs.sergius. Great success. But could I get data from the Earlham Learning Spaces system which is Elgg 0.92? Initial attempts to use the RSS feed straight from the blog were unsuccessful. Having slept on the problem I suddenly remembered that there was a ‘html/RSS’ export in the weblog section. Using this to create a local file and then uploading this with the Import:RSS function was partly successful. Most entries were recreated but there was an annoying string
prepended to every blog entry. When I removed all these strings (and the terminating ]]>) the data was successfully sucked in for all blog entries. And that was not all, the keywords were successfully mapped to categories.