I just saw a very exciting blog post from Stefan Goßner regarding the April 2009 Cumulative Update (CU) - with this update you can now use backup and restore to move site collections between farms: http://blogs.technet.com/stefan_gossner/archive/2009/05/01/red-is-green-up-is-down-and-the-unsupported-suddenly-becomes-supported.aspx.
So first off, yes there is an April CU even though SP2 just came out a couple of days ago (think about it - SP2 has been cooked for a while but they’ve been testing, writing SDK docs, etc., etc., - in the meantime the team has continued working on new updates). I strongly recommend that you install SP2 before you install this update!
So what’s the change that makes it supported now? Anyone ever have to use my gl-fixpublishingpagespagelayouturl command to fix page layouts that were absolute and pointing to the wrong server? Well, this is the primary fix that Microsoft has made so that site collections (specifically those that use the publishing features) can be moved across farms. Note that I suspect that my command will still have lots of uses (I need to do some disassembling to figure out the specific change - good chance my command won’t be needed anymore but I doubt it).
Some more information about the April CU can be found here: http://blogs.msdn.com/joerg_sinemus/archive/2009/05/01/should-i-install-sp2-and-or-april-cu.aspx