I had the amulet on and tried to marry Lydia, it did not work. I went outside and found a hot redhead and married her instead. I had ran an errand for her before so she already had the hots for me. Plus you shouldn't marry where you fish; or something like that.
Somebody mentioned exchange Lydia's armor. While I could exchange her weapons I was unable to upgrade her armor. I would come across equipment greater than mine and try to give her mine while I wore the new stuff and it would just sit in her inventory.
Lydia I let go however she hangs around my Whiterun house still begging to serve me. My wife didn't like that much so I moved her to my Riften home. Then when I came into some money and bought the Solitude home she made me move her there. I have a thane there as well and I haven't heard any complaints from her BUT I think these two are getting along TOO well, if you know what I mean. I come home, she gives me my share of the money; I sell her some stuff extra and she says "good bye my love"; like she wants me to leave or something.