My thoughts on this move:
I would personally rather see Val Majewski in RF with Jay Gibbons doing 1B/DH duty. Majewski is an actual legitimate prospect for RF, much better than Gibbons defensively though Gibbons showed more improvement in RF than at 1B. It would also afford Majewski more playing time as there are only so many RFers on the ML-ready team (Gibbons, possibly Conine or Matos) while 1B is much more crowded (Gibbons, Conine, Millar, Lopez).
But, the team may have a point. Gibbons staying in RF all year allows him to concentrate defensively on one position, as stated before his best at the moment. Corey Patterson and Luis Matos will either split CF or Matos may man LF alongside Patterson, giving Gibbons some breathing room (though Patterson really isn't a world-beater in CF).
Majewski, the Minor League Player of the Year in 2004, had a rough 2005 marred by injury, will need a tremendous spring to avoid being sent down to AAA this season. The team probably figures Kevin Millar and Jeff Conine won't be with the team any more than 1-2 years, and you may throw Javy Lopez in there as well--so by then 1B will be clear for Majewski to take over.
I can certainly live with the decision. I'm sure the 6'2" Majewski will turn out fine defensively at 1B. The only question will be his hitting at the major league level at a position that IMO has recently turned out even more hitting-intensive than corner outfield. If Majewski can return to 2004 form that shouldn't be a problem.