I love chipotle mayo... but I'm not too fond of canned chipotles in adobo. If you can find them (or make them yourself), I also recommend just using chipotles proper (i.e., dried and in a bag, not canned in adobo sauce). In the can, they take on mostly adobo flavor and lose a lot of the smokey chipotle flavor.
When I do mayo with the dried, non-canned chiles, I use 3-4 chipotles and cover it with about 1/3 cup of boiling water. I cover it for about 20 minutes. After that, I take them out, discard the seeds, then throw them in a processor with a bit of the water, about a cup of mayo and a pinch of salt. It makes for a really good, deep chipotle flavored mayo.
Anyhow, that's just me...