Hello,
I've just started to use kde4.3.5 that comes with slackware64-current.
I've always used kde3 "just" because I can let the autohided panel to appear when the mouse hits the opposite side of the desktop (I think it is a sane behaviour to avoid to accidentaly unhide it while I operate on kdevelop tools buttons near the location of the panel), so I looked for the same feature inside the new d.e. and I couldn't figure out how to get this basic, but powerful, feature.
I really don't understand why people still use unhide when the mouse hits the screen border where the panel resides...maybe I am wrong, but the other way is really easy and fast when coupled with high pointer acceleration and makes the panel appear with something like a fast "mouse gesture".
I think it would be a good thing to re-enable it.

I can see both sides of the issue of having the unhide area be the screen edge with the panel. On the one hand most people will find it is the natural way of finding the panel - move the mouse to where the panel will appear to find it. On the other hand I see that it does become obnoxious if you are working with buttons or other content next to the screen edge containing the panel.

There was a request recently added to BrainStorm to try and mitigate this by requiring you to actively push at the edge of the screen for the panel to appear. You might go take a look at that and/or submit another idea for this functionality that you request.