I know anecdotal evidence is not any kind of hard evidence, but fwiw its something we've done with our LO- actually, he insisted on it and loved it and would bounce away like a crazy thing. So far he seems to be fine.

You might be interested in looking at some of the research on jolly jumpers, because there are similar concerns about those (it being much the same action). There was a fairly detailed thread a little while back somewhere on here about them, and it seemed the general idea was that while you didn't want to have them in a JJ (or holding them standing on their legs) for an extended period of time, it was fine for a while. The other thing to watch was that they take their weight as much as possible on their whole foot rather than their toes. The thread was quite good if you want to find it, or just google about jolly jumpers.

HTH!!