In reply to The New NickB:
I have 10 pairs in regular use.....
2x Adizero Tempos -- I have only 500kms on each and they're close to retirement, as I can feel it in the knees after a long run.
2x Adizero Boston 2 -- lightweight trainers. Prefer these now to the Tempos. Good all-round shoe, did my last marathon in a pair.
1x Adizero Ace - light all-rounder, lower profile than the Bostons
1x Adizero Adios - 10K/half racing, may use them in next marathon
1x Adizero Mana 5 - for tempo runs
1x Adizero Rocket - for track workouts
1x Adizero Pro 4 - for track workouts
1x Salomon Speedcross 2 - for trails/x-country
I tend to stick with the Adidas Adizero range as I find they size consistently for me and I get them cheap online regularly (about 50 quid a pair) when they change the colour of the entire range (which is twice a year!!)... I run about 100km a week and don;t tend to get more than 500km out of shoes before my legs tell me it's time to retire them.
I also rotate a lot never wear the same pair two days in a row -- that way I have a little pain spread all over my legs as opposed to a lot of pain in just one place