There has been an ongoing discussion in the InDesign forum about how the new native cross referencing in CS5 seriously bogs down the application if you have a lot of references. I usually don't use a lot of cross references, but I'm currently working on converting books into ebooks, and I'm trying to make use of the cross references to make jump links between locations in the ebook. However, I've noticed that when working with a book file, the document to document cross references do not work in the exported epub file--even when used for something as simple as a TOC. It's a lot easier to create cross references than hyperlinks, but now that I've created hundreds of them in one particular book, I'm wishing I had hyperlinks instead. I know that Teus de Jong wrote a script that turned hyperlinks into cross refs, and I wonder how hard it would be to do the reverse . . . turn all cross refs in a set of open documents into functional hyperlinks that would work when exported into an ebook.