Pirates Prospects has a discussion of a report appearing online now from The Sports Xchange about the Pirates' continuing negotiations with Francisco Liriano. The bottom line is that the Pirates want him to sign a minor league deal and he wants at least one guaranteed season. There seems to be some issue over the ability, in a major league deal, to reduce a player's salary for time missed. The Pirates believe Liriano will not in fact be ready to start the season.
I don't really understand the problem about reducing his salary. It could be handled simply by including incentives based on the number of starts. If that's the holdup, it seems more likely to me that the Pirates are really concerned that Liriano may be unable to pitch for, potentially, most or all of the season. That would certainly make the possibility of a guaranteed year a problem at any significant base salary.
The bottom line, if this report is accurate, is that it's far from certain whether Liriano will sign with the Pirates at all. Hopefully, they're considering other alternatives in the event they don't want to go into the season with Jeff Karstens and either Jeff Locke or Kyle McPherson locked into the rotation.