From the chief pilot at last month's BALPA EOC conference in London: a number of crews are routinely seconded to Ryanair during the winter months and then come back to XL for the following summer charter season (unless of course they are on temp contracts anyway).
Since XL and Ryanair do not share operating bases, I would think that the rumour that they are operating away from their bases rings true...
The Miami Air subcharters were off the cards this year.
Cheers