I didn't think I would ever be able to do more than 5 or 6 to be honest. I did an 8 mile run 2 weeks ago, and was planning a 10 last Saturday but it was rained out. I've found that the key is just doing it, no excuses for skipping workouts. As a coworker who is training for a marathon says, you can't fake the miles. It really becomes mental after the first mile or two - just being willing to keep going, even if it feels like it's a crawl.
You're right about building up mileage - I am in week 6 of this training, and my mileage has increased every week up until this week, and next week it's back to the regular schedule. The most pain I've had is some mild soreness in my arches, but that's subsided with some regular stretching. So far, no knee or back pain, which is where I'd always feel it when I running less often.
Back to the Prestige MP. Should have never deviated.