There seems to be a strategy to extend the value to those people that have shelled out for X1800 parts, by allowing Crossfire to work without master hardware, but only on Radeon Xpress 3200 -based mainboards.
It's set to be announced after CeBit, and looks like being workable with the entire X1800 range, from XL to XT and possibly All-In-Wonder to boot. With X1800 XL at £170 just now, which seems to be price competitive with GeForce 7600 GT, X1800 XL Crossfire without master hardware suddenly looks mightily attractive.
You'll just need a supporting driver and two of the boards you want to run, with no consideration to a master board, providing you have a Radeon Xpress 3200 mainboard. Xpress 3200 offers enough lanes in its northbridge to let you run a pair of x16 PCI Express slots concurrently, with the bus traffic not having to walk any other interlink or bus connection.
It's up and running right now, seemingly without issue, so expect ATI to announce something soon. More on this bean as it sprouts at Europe's premier IT tradeshow in the next couple of days....