Know there is a lot of religion in the Mac v. PC wars, but at this particular juncture, unless you really, really need to replace your unit now, I'd wait until June to see what the next jump in screen technology yields. While still totally rumor, the MacBook Pros are probably going to be refreshed with the new intel processors, which is of some value, but from a photographer's point of view new screen technology is looking probable as well. Best guess is an announcement on or near the Apple developer's event in June.
Mac rumors are a dime per 12, but the screens on the new iPad and reports of supplier ramp ups of new tech, high-res displays in Asia are giving a lot of credence to a major jump in color gamut and resolution that could be significant. Once Macs have it, then PC manufacturers should come along shortly with similar offerings. Know waiting for tomorrow's technology is a bit of fool's errand, but this one is looking like a potential game changer for folks who edit on laptops.