I'm finally returning to work on XRay II full-time and plan to release a feature-complete public beta together with Leopard (Mac OS X 10.5).
On the developer side, Leopard has so many behind-the-scenes facilities - and some that have changed significantly - that keeping XRay II able to run on both Tiger and Leopard may entail significant extra work and cutting back some features I'd love to include. Current estimates indicate that 90% of users will migrate to Leopard before mid-2008. 95% of XRay users are on Tiger already, and I'm sorry to say that it'll be impossible to support XRay II on 10.3 or older systems anyway.
Still, if a significant portion of users request Tiger compatibility, I'll have to do it. So please respond to this poll and comment below if necessary.