My experience is doing this on a 97 delsol vtec.
I request this gets stickied.
I want to start off by saying that I have searched a lot. What I found was many threads talking about "the washer trick" for rear camber adjustment instead of buying adjustable links. The issue I ran into, was burried deep in these threads there are suggestions on how many washers to use but no direct measurements and results.

So here goes,
The car is Lowered on Skunk 2 coil overs. After lowering I took it to have the alignment checked to see how much negative camber I have. The picture below is after I added 2 washers to the left side rear to bring the camber out.



As you can see from the next picture the left rear camber was -2.1. The reason I chose to bring the camber out was to match the passenger side. I did not like having that much difference between left and right because anything over half a degree can cause a pull/drift. (I am just talking about rear camber here. I know there are other things in this alignment that need to be addressed that can also cause a drift or pull)


In conclusion what I have found is that using 2 washers will give you between .8 to 1.0 camber adjustment. The reason there is a difference is that all washers are not created equal (some are thicker than others) and that small difference can make a small difference in alignment specs.

The washers I used where about 2 mm thick. I used 2 washers per bolt = 4 total needed which gave me about .8 degrees of adjustment.
P.S. something else that was unclear in my searches was should I replace the stock bolts with longer ones. There where a lot of opinios on this.
so here is my opinion and reason why.
If you use more than 1 washer please replace the bolts with longer ones. That is the safest thing to do. Grade 10.9 M10_1.25x40mm is perfect for using 2 washers per bolt. As you can see in the pictures below, 2 washers take up alot of threads.
I know there are alot of people that have used 2 washers and did not replace the bolts and have not had any issues so please use your best judgement.

As you can see I did not (SLAM) the car. I just wanted to take up some of the wheel gap.