Originally Posted by jm01
because there should be no wobble in the cog set when the wheel is spinning...a broken/worn hub, a loose lock ring, a bent/broken axle could be causing this...even at the low end there should be no or minimal wobble...could be a sign of a problem or a lack of maintenance, but you'll be putting lateral strain on the chain, accelerating it's stretch and wear...and depending how bad it is, it will accelerate the wear on your cogs, and possibly your chain rings
I found this out when a loose lock ring finally let go and my cassette fell apart on the trail
I think a loose lock ring "wobble" looks a lot different than what he's talking about. The slight gyrating of the freehub body is pretty normal, even on some higher end hubs.
It happens on 100 dollar wall mart bikes to 8,000 super bikes, depending on the spec. Like everyone else said, don't sweat it as long as everything is in otherwise proper order.