I think it's easier to move a starter to the pen mid-season than to do it the other way around. Wainwright was a starter in the minors, came up to fill a need because he was the best arm they had for the role, and eventually thrived as a starter at this level. Joba's ascent to the big leagues started similarly, but then they tried to ease him from relieving to starting mid-season in 08, and he's since gone backwards. I think if you commit to using Mejia as a reliever right now, you had better commit to keeping him in the pen for all of 2010. Among other things, that means you need to be confident he can stay up in the majors all season; otherwise, assuming you see him as a starter long-term, you've cost him a year of development. Personally I've been wavering on my opinion of his ability to handle it, but Parnell survived in the Mets pen last year after making a similar transition. Mejia is more talented than Parnell, so lately I've been leaning towards bringing him to Queens.