Training for a 50 mile run (with some walking- ha)

I did a local 50-miler on 3+ months of ultra/IM-Base training last year.  For me, the ultra was a long training day, and a chance to work on the mental aspects of "running" 11-12 hours into the day (like I expected for the Ironman). 

My "long runs" were 17-27 miles (3-6 hours) and made up the bulk of my weekly running volume (I'd run 3-5 miles once or twice a week).  I was also doing some 2-3 hour rides on the trainer.  For the race, the first 30 miles went pretty well.  For the last 20, I walked more than I wanted, but still felt pretty good at the end of the day.  (My first two 10-mile loops were right at 2:00, the third was 2:18, and the last two were 2:30-2:45)

The more days you get get 20-30 miles (walking if you have to) leading up to the race, the easier the day should be, but an ultra is all about going in with a good strategy to finish and then sticking with the strategy in spite of feeling like you should be going harder early in the day.  I probably worked a little too hard the first two laps trying to hold 2:00 with the mud, but was never in doubt about whether I *could* finish.  (I was ready to pull the plug rather than risk IM training with raw feet or a muscle strain). 

Here's a good link for you to set up a training plan:  http://www.scrunners.org/ultrasch.php

They don't have 2012 in the system yet, but you could just plug in 2011 to get an idea of a training plan specific for your distance.  One of the most important factors in conditioning your body for the miles is to do back to back long runs with recovery the days immediately before and after.

I agree that you should throw in a 50K and train through it (no taper unless you plan to actually race it).

Good luck!