Observation:
Since install I've made 2 road trips, one 700 miles and one 300 miles (today). Around the 200 mile mark on both trips I noticed 2 things - (1) that there was a very subtle noise which I'd describe as low-rev venting. I talked alot about this elsewhere and it was the reason I bought the DV+ after my turbo upgrade, and it eliminated the noise. However after a few hundred miles a venting noise returns....and, (2) that the car studders when you try to go into boost.
Now both times, both of these issues were cleared up by a few WOT runs in 2nd and 3rd gear.
My theory is that when the car is in cruise control and/or asking for about the same level of boost for hours at a time, the valve sticks a bit and causes these two symptoms. After a good thrashing (the WOT pulls) the oil re-lubricates the valve and all is well. Of course it stays lubricated under normal conditions because it's constantly opening and closing, but not when maintaining the same speed for 100s of miles.
So maybe if you have these issues you'll know you're not alone because of this post. In the future when I anticipate driving a long way as such I'm going to periodically drop it into 3rd and floor it to redline to hopefully prevent this sticking and keep the valve lubricated.