Have had the Rhinoskin leather flip case for my 600 for two days now. I was going to return it in leiu of another solution but I think I'll hold onto it. For anyone considering it, here's my review:

PROS:
Protection aspect seems great. The leather is of good quality and cushiony enough to absorb a drop I would imagine, although (thankfully) I haven't dropped it yet.

The flap covers the screen and attaches via snap at the top of the 600, and flips downwards. Inside is a SIM card holder, and I think you can put a credit card in too.

Openings are available for the top buttons, side buttons, headset port, sync port, camera and stylus. The keyboard --and entire front of the Treo--is exposed for easy access once you flip the cover.

It comes with a belt clip which clicks in sturdily, and one GREAT feature: You can remove the belt clip knob on the case if you want to revert to "flat" storage. And, it is much more comfortable to wear than the clip on my old Krusell case for my Treo 180-- that stabbed into my side and was quit painful. The clip swivels, and already I can tell you it feels less clumsy than my 180g hanging at my side.

Nice addition: RS products come with a Lost/Found feature-- you stick a special serial no. on your phone. If lost, finder can return to RS for reward and can track you. And it only costs about $15 you plus s/h. Give a cookie to the RS marketing person who came up with this promo idea.


CONS:
Probably the biggest problem is having a long flip cover hanging down from your chin when you're on a call---and the snap part of the case sticking in your ear. I looked at the EB case, similar to RS, which had a removable flap but didn't buy based on bad reviews here. If RS made a removable flap, I think this would be the best case around.

The alternative would be to remove the phone from the case, but it isn't a exactly smooth task because the side buttons get caught in the leather's opening. The first day or so I could hardly get the phone back out, but it's loosened up a bit and is better.

Also, snapping lid shut was difficult but has improved with break-in.

Speaker holes don't line up exactly. No major setback noticed as of yet.

The belt clip release button is sticky. I don't find this is easily workable as the Krusell clip I used to have, which had a prominent release button. The release button on this RS is kind of hidden and has me fuumbling for it a lot.

The case adds some bulk but not a tremendous amount. It won't fit in a cradle with case on.

All in all, a great case so far in many important respects, but could use some smoother access which I think is more a matter of fit. Perhaps after breaking in it will be smoother.