We used bushings whereever we could last year, all throughout the trans and drivetrain as well as the wheels and most any other mechanism that moves. Ball bearings are great if you expect to put the machines into extended service, but for the amount of time that we use these machines, the added weight of the bearings doesn't seem warrented.
Andy is correct in stating you need a good surface finish on the shafts, but you can easily achieve this on a lathe with 400 or 600 grit paper or a centerless o.d. grinder.
We didn't use your average bronze bushing in most areas either. We used Ampco Bronze with is harder and has better lubricity than the regular bushings. You don't need real tight tolerance on the shafts either. In fact the looser you can run them, the less friction the system will have. Also use either White Lithium or Graphite for lubrication.
This year it is our mission to eliminate all ball bearing from the machine and use Ampco Bronze instead. I am however, adding Roller Thrust Bearings (which are very lite!) to each side of the hub on the wheels. This should reduce any friction generated by the scrubbing which occurs due to the 6 wheel drive style chasis.
