Always some answer like this. Apple may not be to outspoken but the are enough indirect clues. Intel has a very strict roadmap and unless they run into problems with the 22nm node they will launch Ivy Bridge in the first half of next year. Which in the past meant they aim for January. Since Apple's MBP are premium products they cannot simply sit tight while every other company releases Ivy Bridge Notebooks. Thus they usually refresh as soon as they get enough chips delivered from Intel.
If all is normal, then a refresh is definitely within the next 12 months. However, with NAND chip production under stress from the Japanese earthquakes, it's hard to say if anything will be back on track over the next 18 months.