I haven't but I know people who have used Yasso 800s and found them to be a pretty good predictor of marathon time. Note that they have to be done at a particular point in training and following his specific method to work as advertised.
I recently replaced a 7-mile pace run with Yasso 800s just to see how I'd do. I'm training for the Marine Corps Marathon at the end of October, so I'm still kind of mid-season. Anyway, I did 10 reps of 800s with 400 meter cool downs in between. Also, I kept speeding up a little at a time instead of staying steady because it was going so well. My goal was to do ten reps in 4:14 each time, but ended up starting at 4:11, working down to 3:57 by the 9th rep, and letting it all hang out with a 3:48 on my last. That was very encouraging, since my median and average reps were around 4:06 and 4:03, with a max of 4:11.
I've heard that these are an accurate predictor, and time will tell, but I still don't think I can pull off a 4:03 to 4:06 marathon. My half-marathon PR was 2:01, set in May, and I currently struggle keeping up with marathon pace (based on a 4:05) on my 7-8 mile pace runs. But I did my Yassos on an unusually cool morning for August (about 60 degrees), while my pace runs have generally been in 70-75 degree weather.
Also, as every individual is different, I seem to be relatively slower on longer races - when I look at the Runner's World training calculator, I seem to slow down at longer distances more than the average bear. For instance, my 5K PR of 24:33 indicates that I should be able to do a 10K in 51:08 and a half-marathon in 1:52:44, but I can't break 2 hrs on a half or 52 min on a 10K.