Actually, I have always thought that these guys are weird. But maybe, thatc because I am on "producer" side. I think opinion of someone who is not on both sides is more relevant then mine, but heres my opinion anyway. Registering for faves, watches and comments sounds dummy to me. DA is place to share art in the first place and then goes here all the fun stuff, friendship and so on.. There is no need to register if you want to download icons, wallpapers or freebies, with the exception of mature content. So I dont really see the point why register here. I am sure as hell that there is some kind of 3rd party utility that alows you to show your bookmarks as preview images... on the other hand, finding something is in these times really easy, but some people are lazy to spend even 20 minutes for it. So when I more think about it, I see it like this: While some of us are here to get feedback on our work, others are here to give it. And I dont see nothing wrong in that. But honestly, show me one person that registered to DA for comments like: "Super, awesome, ulallala work I love you, big kisses!!!". Nope.. thats certainly not kind of feedback we were looking for here. We look for constructive comments from guys in our field. If I want to know opinion of other people, I can just ask my mom or girlfriend and it will be the same. That not means that we would be ungrateful for feedback we get from these users. But sometimes you just dont want to show 20 pages of content about how your work actually works and for what it was made for. You want to hear opinion of and artist, designer, developer, creative mind with big cofee and huge strong glasses, that can help you get better and have experience over those years.
That pretty much sums me up. I made an account so I can watch people whose stuff I like so when they make new things, I can see them easier then having to go on to their page daily and see if they've made anything new. I favourite things because if I like it then it deserved a favourite, right? If I just bookmarked it all instead, my bookmarks would be full and most likely messy, with an account it's all in one place and it's organised so I can see what I want to see easier.
As said, I don't understand why people would view it as at all creepy. I'd see it as a good thing actually, that people have joined purely because they like what they see and want to watch that person for new things they make or give them the favourites they deserve.
I am a perfect example of what you are describing here, but my favourites and watches are for my own personal use. I like to get awesome free stuff like themes and wallpapers,and icons. Everyday when I sign into deviantart is like Christmas, deviantart is an amazing site and I love the fav and watch feature.
I do not see an reason why would would find these people "creepy", I do not know what world you live in but there are always more consumers than producers, and this type of activity shouldn't come as a surprise to you.
I liken this to YouTube. While I have an account there and have posted a clip or two, and am subscribed to a select few people, I have many favorites. Sure I can bookmark. But I fave because it collects them all on my channel, with large thumbnails, I can arrange them to my liking, and they are easily accessible at a glance.
I can totally see someone faving stuff on DA for many of the same reasons. What I can't understand is what some folks actually are faving. One favorite is a spectacular landscape and the next fave is some doodle not fit for a mini-fridge door.