In November of 2007 I published a blog post
extoling the virtues of a new STSADM operation, mergecontentdb. At the time, it was the coolest thing ever. Now, after 16 months of use, it's come out that in some, very rare circumstances, mergecontentdb may fail and may result in data corruption
. Because of that the SharePoint product team
has suggested using it with extreme caution, or better yet, don't use it at all. Their blog has a method using Batch Site Manager
to do the same thing, but without the pesky data corruption. I would imagine there's a fix in the works, so if you can hold off moving any site collections, I would recommend it.