an interesting thread and hopefully I can add that good times can be done off relatively little mileage and some training insight. I started running after 11 years off although I had kept active through swimming and racket sports and unlike some never had to shift weight first- i think i was 9st 9lbs when i started back up. As some have commented once the weight comes off the times tumble.
May 07 ran a 10k in 38:11 off 1 month of 90miles of steady running
improved to 10k of 35:03 and half of 1:19:10 off av. 20-25 mpw in 07
after 6months of 30mpw last year half down to 74:41 and 10k down to 33:19. Although my 10k has not improved after 14 months of 30mpw I finally got my half down to 73:31 last month and I think my 10k can get below 33 this summer. This slight improvement while maintaining the same mpw I put down to a full xc season this year- so in effect a real hard run every 2 weeks.
pluses: lower mileage means I am rarely tired for sessions all of which are run sub 6:40 including a 10-12 miler at the weekend or a race, tempo (5:40 pace) or long rep intervals (3:10 1k pace) midweek and then a couple of steady runs . In my favour; I'm a skinny rake 5ft9/127lbs, ran constantly at school, must be an efficient runner and rarely get injured due to the low mileage. I also advise all to run xc as it's a great stamina and strength conditioner.
the minus side is that when i went on holiday for 2 weeks last October and did one run, put on 7lbs, it took near 2 months to get back to full fitness as i guess I don't have that mileage base to fall back on.
Work and home commitments mean I can't train anymore and while I'm still seeing improvements, albeit more slowly, and thoroughly enjoying my running I see no reason to increase mileage. There is a nagging doubt on what I could achieve with higher mileage but then maybe the enjoyment would go if i was out every day and getting nobbled/knackered
its flat! and not very scenic but a great race hence why I'm thinking about doing this for a second year in a row as I have the sub 77 time to achieve. It was hot last year but had plenty of water stations laid on and very friendly support.