Linking multiple Analytics accounts to Adwords

Some handy info here from the GAAC* Program Google Group.

The question was posed that while it is true that you can link several adwords accounts to one anaytics account by having these accounts pull in the "cost data" from many Adwords accounts, people were wondering whether it is possible to link several analytics accounts to one adwords account?

The answer provided was that the "linking" that adds the AW cost source to GA and lets you see GA data from within the AW interface, works in certain regards on a 1-1 basis only.

Adding cost sources, though, can be done from multiple AW accounts to multiple GA accounts, all you need is a skillful Google account manager to do that for you. After this has been done, you can, as you probably already know, go in every profile of every GA account you have added a cost source
to and apply/unapply it. This type of setup can be seen below with a live screenshot of an Analytics account with 2 cost sources attached but only one of them "applied" with the tick:

Apply Cost Data GA

One important thing to bear in mind though: Only the first (primary) adwords account you link will enable you to pull analytics goals to adwords. The others will be secondary cost sources. This primarily linked GA account would be the one that appears when you click the GA tab in Adwords:

Google Analytics tab in Adwords

In some cases it is crucial "who to link first" i.e. first linkage you do manually and second via account manager - just make sure the first linked account is the main GA+AdWords activity in order to best integrate.

*GAAC stands for Google Adwords Certified Professional.