I think you might have a problem with the shoe tracker. I entered a 5 km run and a new pair of shoes for the 19th Aug. I put in the distance as 5km but the shoe tracker showed it as 4.83km.
Think I've had the same problem with the shoe tracker myself. If I look at:
http://www.mapmyrun.com/gear_tracker
I see my single pair of shoes with a total usage of 92.38 km. If I then click on the "workouts" link in the Actions column, I see a list of all the workouts I've ever done in the shoe, with the heading "Results (16 Found | 0 Total kcal | 71.77 Total km.)"
The latter is the correct total. Being a geek, I have to speculate on the cause. I suspect this stems from a bug in the workout entry form that has since been fixed - I think the page of the form titled "Step 1: Workout Summary" once messed up the "Total Distance" field, and recorded some distances as miles instead of km even though I said km, and I had to go back and fiddle with each run to get the distance recorded in the correct units. Looks like the form bug there got fixed but the erroneously saved distances survived somehow - probably because the total for a pair of shoes is (for some performance-motivated reason) stored as a field in the database rather than added up from the individual runs each time.
It's no big deal once you know which is the correct total, but if I'm right about the separate field thing then the database admin could fix it fairly easily by hacking together a script to recompute the totals for each shoe from the individual runs done in that shoe, or just by always doing the sum instead of keeping a copy.
If anyone else suffers from this and is really bothered, that person might like to try removing all their workouts and re-adding them from scratch - but then if the author of the code didn't enforce a ">=0" limit on the distance run in a shoe, you might just find your shoe total goes negative.
That said, don't look a gift horse in the mouth - apart from that minor niggle the site's great, and I'm grateful for all the work that's gone into it.