Are there any long term durability issues with the Armalite AR-180B rifles?
I was a little concerned with the polymer receiver and how they will stand up over time.

be careful opening up the receivers because the lower can crack at ghe pivot pin. I would pass unless you can get it cheap...

$600 and it's in like new condition.
I already have some AR rifles/carbines but it interest me because it uses same mags and because it's not a AR...something different.

Some lowers can if they are slammed open. 
There are repair pieces made for if it happens. 

$600 for a like new AR180 sounds like a good buy to me.

Here is an awesome replacement lower made from 7075 T6 http://www.nodakspud.com/NDS-18S.htm

Or the cheaper (and non-firearm) alternative:

Pivot Repair Section

 

I honestly don't know why anyone would go that route (a piece of 6061 aluminum epoxied onto plastic) when you can get a full one piece 7075 lower receiver.

Is that a declaration and not open to outside views, or are you looking for actual reasons that people would buy it (the small repair piece) instead of the AL lower? 

To clarify - The StormWerkz piece is a viable option (it used to be one of the only solutions) and substantially stronger than the factory plastic lower.  As such, it deserves to be added to the discussion so yes, I am open to outside views.  

If my friend had an AR180B and wanted to go the StormWerkz route, I would have to at least point out there is a better option since the one piece 7075 receiver is substantially stronger than a piece of 6061 epoxied to plastic. I wouldn't have any problem if he wanted to go the StormWerkz route anyway.  

If I had an AR180B I wouldn't even consider the StormWerkz option if there was a one piece 7075 receiver option.

The SW option is 80 bucks and has availability. (It epoxies AND pins in place) 

The Nodak AL lower is 265 and not always available. 

Sometimes people want cheap guns because they're cheap, getting a cheap gun and then throwing 260 bucks at it when 80 would do is a better option for some people. 

Quoted:
The SW option is 80 bucks and has availability. (It epoxies AND pins in place) 

Did you know that 7075 is approximately 67% stronger than the 6061 the SW section is made from?    

The Nodak AL lower is 265 and not always available. 

The NoDak website shows that their AR-180 receiver is in stock and ready to ship - http://www.nodakspud.com/NDS-18S.htm

Sometimes people want cheap guns because they're cheap, getting a cheap gun and then throwing 260 bucks at it when 80 would do is a better option for some people. 

Everyone has different views of what is cheap or what is inexpensive.  Whichever path anyone chooses as they determine is right for them is fine with me.

Did you know that the strength of a solid block of 6061 aluminum with a 1/4 inch hole in it is about the same as the little piece of stamped steel in the original AR-18, and the three little pins and glue (depending on the type of glue) have about the same shear strength as the three spot welds of the original?

I pre-ordered mine when first announced at the SHOT Show.
It sat in my safe for years unfired.

I pulled it out and the lower was splitting in half about 3/4 inch just from sitting there.

Sandy Hook happened and I sold it for $700.

Too bad because it is a nice design for a rifle, just bad execution.

Wish I had known about the replacement receivers, but not sure if I would have put more $ into it either way.

Can you admit that the 7075 receiver is better?

Man you guys are emotionally attached to the SW piece.

It doesn't take much searching to find that the original steel spot welded lowers had their own strength problems.

And with that I'm out of this discussion as OP has plenty of info to make a decision.

I'd let it go, he needs this one apparently. 

I picked it up last night for $600 and it came with 30 round P Mag and a 20 round Colt aluminum mag and the Storm Werkz extended receiver rail.
The rifle looks new and inside was clean.  Owner said he fired about 30 rounds when he originally purchased it in 2005 and then just put it away.
I shot about 100 rounds this morning and it was 100% reliable and groups at 50 yards were decent (consistent 2.5"-3" group with Federal Eagle .223 FMJ).  One issue is that the groups are about 6" to the left when the rear sight is centered so I guess the front sight is not strait but I don't see a problem as the FSB is held by pair of screws.  I also noticed the increased felt recoil compared to my lightweight AR carbine which is about same weight (6.0 lb.)  I guess the increased felt recoil is due to the heavy bolt assemble on the AR-180B.  

I see the concern people have about the front pivot and it's potential breakage if abused during disassembly.  I'll just have to be careful when I disassemble the rifle.