If you're referring to the thank-you notes section listed on a contributor's profile page, then the answer is 'no'.
Thank-you notes are still listed on your profile page, as you can see here with my profile
So, to see a thank-you note you sent to someone, simply visit that contributor's profile and check it out.
Mind you, contributors have the ability to delete notes they got from, as well as notes they sent to other contributors.
Now, to send someone a thank-you note, simply click on the little read heart that's located to the top-left of the answer frame
At this point, the contributor gets karma points in proportion to his or her contribution to the answer, and a thank-you note window becomes visible.
This is where you can write a thank-you note. Once you're finished writing the note, click on Send. The thank-you note will then be visible on that contributor's profile page.