I LOVE my otomix cross trainers for lifting!!!!!!!!
I have the versa-trainers!
http://store.yahoo.com/otomix/otomixfootwear.html
These have support on the bottom. I also have custom orthodic inserts for the heel to arch section, then I cut up the regular shoe padding to cover the arch to toe area. I had lots of bunion surgery 10 years ago and I got my orthodics then. Otherwise the area across the top of my foot starts to ache unendingly and I'll go back to having those wonderful "old lady feet" where your big toe curves inward with the big ball of the foot sticking outward and then you end up with all the other toes trying to counter balance and becoming hammer toes. Nice image huh? Sorry. Its hereditary so I didn't have much choice. At age 25 I had the same surgery most older women have.
So my point being good arch support is CRITICAL. I was using running shoes with my orthodics for training last year and they sucked - the otomix or at least something with a solid ankle and foot seem to be much better for lifting. I can also use the otomix for cardio, tho I rotate between those and two other pairs of leather cross-trainers. My feet will start going numb after 30 min on any non-sitting cardio machine. I've gone the "get new shoes" route already and it didnt' change. So basically I think its just repeated putting pressure on the same point of your foot (e.g. the ball of your foot) for 30 min at a time that makes it go numb. So I just rotate every 20-30 min between machines and try to keep standing machines separated by some time on the recumbant bike to help a little.
I also always seem to get major shin splints when I use the treadmill - so I'm really careful about stretching out before using it and how close to leg day or calf day I use it.
When I had my foot surgery, I spent almost a total of 4 months in foot casts getting both feet done (2 bunions, 2 taylor's bunions and 4 hammer toes) and you don't realize how dependent upon your feet you are until you can't use them. It also helps if you are driving an automatic instead of a manual transmission.....
So -- if your feet are bothering you in the gym - DO SOMETHING ABOUT IT! If you screw up your feet now, imagine how much life will suck when you are older! If you think you might have bunion problems or tend to get sore, throbbing moments on the tops of your feet - GO SEE A PEDIATRIST!