Here's a simple solution to your problem- Book your GMAT date. Believe me, once you do that you'll motivated enough to study. Use a top down approach and chalk out a strategy for yourself . One very good way of keeping yourself motivated is to keep participating here on the forum. If you do that, you'll be in the "GMAT world", enabling you to stay tuned .

Great topic, guys - ultimately, I've always said that I fear a student giving himself too much time to spend studying for the GMAT more than I fear someone giving herself too little time. Like you've mentioned, I think it's easy to procrastinate, to lose motivation, to get in the habit of "just doing problems" mindlessly without making specific improvements, etc., and then you also have so much time invested that there can be more pressure than it's worth.

If you do have some time to study and you're concerned about staying motivated, I'd highly recommend:

1) Write it down! If you write down your study goals for each week, your plans for each session, etc., it's that much more powerful than just mentally thinking that "I should...". Writing down "I will" is much, much harder, psychologically, to blow off.

2) Be specific! Don't go into the library for 2 hours to "do problems". Go there to "perform an hour's worth of timed quant drills from OG12 so that I can practice spending <2 minutes per question, and then analyze my mistakes to see which concepts I struggle with under that pressure", or to "practice thinking proactively on SC questions and to gauge how often I just use my ear". The more specific your goals, the easier it is to commit to that session - currently I'm doing some swim workouts each week for triathlon training, and although my goal each session is 2-2.5 miles, I'd go crazy if I didn't break it into segments of 200-500 meters at a time with some timed goals and/or every third rep devoted to stroke technique or something like that. Give yourself specific assignments and you'll not only get more out of each session, but mentally they'll each be different so the variety will keep you engaged longer.

3) Like Rishi said, give yourself an end date. It's much easier to stay motivated when there's a finish line and you know that you have to make progress toward it. Necessity is the mother of invention...if you have a hard end date, you'll find ways to keep yourself motivated just because, well, you have to!