Well I just entered the .308 game by trading into a brand new PTR91.  It's a super sweet rifle and I like the way it looks and feels in my hand.  I've yet to shoot it yet though, so we'll figure out how I REALLY like it when I am able to make it to the range with it.  

What do you guys use for a sling?  Anything that works better than another?  

What all websites are there for parts/accessories for these types of rifles?  I've already been to hkparts.net I believe it is.  Is there anything else I should go check out?  

What do you guys think of your PTR's?

ETA:  Also, I don't like that I can't reach the mag release like I can on my AR without moving my hand significantly.  Is there some sort of an extended mag release or something along those lines for these rifles?

Check out robertrtg.com for parts. I think he also has German made .22lr conversion kits.

There is a product known as a Tac-Latch that allows you to release the mag from the opposite side of the rifle.

Here's my take, FWIW:
When you're shooting it, pay attention to the trigger.  Then, when you decide you want an upgrade, go here: Bill Springfield.  I have one of his triggers, and his improved buffer.  Very nice "plug 'n play" additions.  
For a sling, I have an Armageddon Carbine sling.  Similar to a VTACs, but I like the slide buckle better, and it has the bungee working for it.
Don't have the paddle mag release yet, but that's next.  I'm in no great hurry, since I have long skinny fingers and can just barely reach the stock mag release without changing my grip.
All in all, I like it.  Not as light as some other 308s out there, but the ergos suit me fine, and it's a nice shooter.  Not too bad on the recoil, and with a decent scope, I'm good out to 500 or so without  too much trouble.
Be sure to post some pics of your baby.  I'm probably going to start a thread, once I give mine a paint job.