This is a good topic. It definitely varies person to person, and will vary a lot depending on what event you are focusing on as well.
Lately my weekly totals have been 10-15% "high quality" miles (marathon goal pace or faster), and then my long run usually ends up being about 15% of the weekly total as well. But I run a lot of miles, so those numbers might look more like 20%/20% if I was running more in the range of 100mpw. I anticipate that the percentage of faster miles I run will creep up a bit in the upcoming weeks as I get closer to my goal race. I'm keeping a more detailed spreadsheet with all that kind of data this year - I think it will be interesting to look at the trends of different training cycles.
25% speedwork is probably a lot - especially if you really are thinking of speedwork as 5K/10K pace or faster. To me that could be a recipe for disaster. But again, it depends on the person - if you are running 40-50mpw, then maybe that is a realistic figure.
And since junk miles were brought up I have to toss in my one of my favorite sayings -
"junk" miles got Bill Rodgers to 2:09