This came by e-mail:
First of all - the road to the border. From Ashgabad to Serdar the road is excellent since it's on the way to Turkmenbashi. Problem starts when one turns left towards Etrek. Road is bad, full of potholes and grooves. But it's still possible to drive ~40-50kmph with an average (not 4x4x) car. There is a checkpoint in 38.502450, 56.192856. Perhaps this is where the border strip begins. After the junction the road goes much worse. Potholes, grooves, lack of tarmac, mud. Sometimes the road just disappears.
There is a looooot of camels which just stand on the "road" and don't really want to move. For us the last 150km took over 12 hours, but we had a problem with our car's suspension. Perhaps it's possible to drive faster with a 4x4 car but it's still terrible. There is almost no traffic. By this time we saw maybe 10 cars.
And there is no gas station. There is only one in Etrek. There are 2 or 3 villages on the way. Looks like it's possible to buy petrol from the locals but we didn't try. Another checkpoint is in Etrek. From this point the road is good (some parts under construction in November this year).
Second - the border. Perhaps it's open from 6:30 and for sure it's closed at 4:30 PM. There is a lot of local traders who want to cross the border but the police took us - as tourists - first. It's a lot of paperworks, but the border police is rather helpful (and greedy of course). As I wrote in one of the posts - this point is called Altyn Asyr but it may be mistaken with the Bajgiran border which seems to be called commonly Altyn Asyr too (I guess it was just bullshit to make us pay, but you can keep it in mind).
Barely anyone can speak english there (we spoke russian but there was one young officer who spoke english fluently). Everything took a long time, they tried to make us pay more money for nothing but eventually I spoke to some kind of superior and they let us go. We had to pay 45$ fuel recompensation extra for violating the route.
They had no data from the road checkpoints (didn;t know where we drove). Also, no problems for not staying in hotel in Ashgabad. There was no personal search and the car search was very cursory. They barely looked at the trunk. This was the turkmen part.
The iranian immigration part was pretty quick but maybe because Turkmens let us go just before closing time. Almost zero car search, we brought 4 bottles of vodka and a lot of pork
No way to enter without carnet du passage. Also, barely anybody speak english (nor russian!) there and they are extremely chaotic.
We had some papers problem and really no-one told us what to do. Police and customs officers were very kind and gave us a lot of tea but they couldn't help us with our issue. Finally there was one guy (perhaps a custom office boss or so) who spoke english but also he was extremaly messy. It took us many hours to solve the issue.
There is a bank near the border and also a bazaar where it's possible to eat sth, buy stuff or exchange money (blackmarket of course). We didn't see any queue to the border from the iranian side. The road to Gorgans is pretty good.
Also, what might be useful. The road through the mountains (between Gorgan and Tehran or just between Gorgan and the rest of Iran) can be closed when a fresh snow falls. I takes several hours before police makes all trucks stop on side and the road service removes the snow.