The biggest functional difference I can see is that the PM9 ships with two mags, but spares are about $40 a pop.   Is another $160 more worth it for the polygonal barrel, non-MIM slide stop lever and a roll mark instead of engraving?  

Is there any significant advantages in accuracy, trigger pull, durability?

Update below.

I have a CM9 and a CW9. To me the extra $150-200 isn't worth it. The triggers are awesome and as far as the rifling do you really need a match barrel on a pocket pistol?  I say buy the CM9 and spend the rest dot the difference on a holster mags and ammo.

I have the PM9, great little pocket pistol but the CM9 is just as good for a little less. Talon Grips make a big difference on the little Kahr.

I have a PM-9...No its not worth the extra money.

When I bought my PM9 nearly two years ago, the CM9 wasn't yet available.
Would I have gone for the CM9 instead of the PM9 if available at the time? No.
I wanted night sights and I like the dove tail FS on the PM9. I don't want a pinned on plastic FS.
I wanted an all black pistol, this isn't a CM9 option.
The added cost of the PM9 vs. the CM9 would not have been a problem at the time had I been offered a choice, PM9 all the way.

The features are worth over the difference in initial costs but most people dont really need them so for them it's not worth it. If you need or want these features then it's worth it.
You cant shoot reloads in the lollar barrel. I believe the barrel will last much longer and be marginally more accurate. Maybe a used pm9? Best of both worlds if you can find one you know is issue free.

Edit- unjacketed lead reloads obviously, sorry.

Picked up the CM9 earlier this week and got a chance to take it to the range yesterday.  Overall, I'm impressed.  The pistol looks and feels like quality.  I understand this is the "cheaper" version, but everything looks very well machined and put together.  The feed ramp is very polished and smooth.  Trigger pull is long, but very smooth.  The trigger itself is wide and very comfortable, making the DA pull even easier to handle.  

I ran 200 rounds of WWB and American Eagle, plus a box of Gold Dots through it.   I was expecting a few malfunctions during this break-in, but none happened.  I didn't do any limp-wristing tests, but did fire a few mags one handed.  Everything fed and ejected without any problems.  Mag catch was sticky for the first few times, but improved eventually.  Accuracy was pretty good.  It's not a match competition pistol, but the two mags I fired at 25 yards were all in the silhouette.

I owned a Kel-Tec PF9 for about five minutes, after they first came out.  It proved to be a total POS and lowered the bar for me as far as pocket nines are concerned.  Before buying the Kahr, I also looked at the Ruger LC9.  Even though it was about $30 cheaper and came with two mags, I still liked the Kahr for build quality, simplicity of operation and a better trigger, IMO.

Now, I just have to figure out the holster options that will be secure, easily accessible and still take the most advantage of this pistol's small size.

I love my CM9. I have 500 rds. so far through mine and haven't had a single malfunction using all different kinds of ammo.

I might try the Talon grips mentioned above though as my Hogue grip slips a little too much for my taste.

I just wish you could get it in all black; but wasn't worth the additional $$ for that privilege.

It's a contrast to an early P380 I owned which had a lot of little issues before I decided to sell it. I might give the CW380 a try down the road if it gets favorable reviews when released someday.

I was leaning toward the CM9, though I've only shot a PM9. But I've been seeing some super low prices on new PM9s and I'll probably go with one of them sometime in the next few weeks. Really is a great little gun.

CM9

    How low are they!
     Seriously though, I've been shopping myself.  Where are you seeing the best deals?

I have the CM40. They do make night sights for it, and I installed them myself. The second mag with the PM is the silly looking extra round mag that defeats the purpose of a pocket pistol. I simply bought two more standard mags. I am still ahead of the game, and I don't care a bit about the roll markings. Gun lives in my pocket, no one sees the markings.