I’ve nearly always heard it as the latter. It’s annoying either way.
Sadly yes.
I wouldn’t say it. When it’s said to me it’s always been “blest.”
I’ve noticed the “I appreciate you” thing too - it really irks me.
I’m in the south now, and if someone tells me to “have a blessed day” my recently learned response is, “well, bless your heart”. I’ve learned that this isn’t exactly complimentary.
Have a blessed day rile you up?
I have a friend who’s voicemail implores me to “Have a Jesus filled day.” Since she knows I’m an atheist and loves me anyway, I left her a message to “have a flying spaghetti monster filled day. May you be touched by his noodley appendage.”
She liked it. Which is probably why I have a friend that has a voicemail message that implores me to “Have a Jesus filled day.” 
Ugh. The Hallmarkization of American English continues.
Have a damned day
Slightly related, when did Americans stop saying “you’re welcome” and start just going “uh-huh”? Or has this always been the way you respond to thanks?
“Thanks very much for your help.”
“uh-huh.”
All Americans haven’t. Just the rude ones; or perhaps the Yankees. 
“But I repeat myself.” rimshot
I don’t think of it as rude, just casual. 
Weird. The closest I get to this is hodling someone’s hand in mine and saying ‘I appreciate your time.’ But it’s only so I can steal their wrist watch.
I have heard “blessed day.” It was pronounced “bless-ed” every time. I did not appreciate them.
There’s a bit more flexibility. Although “uh huh” is rude, other substitutions like “you bet” or “no problem” I don’t have a problem with.
At the moment I’m trying to decide whether I’m more annoyed by “I appreciate you” or by people who, after I answer their question, just hang up. On the one hand not thanking me is rude but on the other hand it spares me from several seconds of having to talk to them, so it’s kind of a toss-up.
My best friend says this at least once a day, for instance, when I’ve done a bunch of things to make his job easier. I’ve never heard anyone else say it, and it’s kind of odd, but his heart is in the right place. He’s just the kind of guy who uses catchphrases.
I find the “uh huh” or “okay” as a response to “thank you” rude, too. I understand that it might not be rude if you’re a United Statesian, saying it to United Statesians, but when you say it to a Canadian, you sound rude (it sounds dismissive to us). I don’t get bent out of shape about it, though, because I realize that people saying it don’t know no better.
I think my response to “I appreciate you” would be, “You do? In what ways?” I’ll have to work on a response to “Have a blessed day.” “No, thanks.” comes to mind.
I beg to differ-just as many rude folks down south as up here.
I hear “have a blessed (pronounced blest) day” every day–from the black folks at work. I have no idea if this is a Southern thing brought northward or if it’s a common African-American thing, but it makes me grumpy to hear it.
I work in a hospital–some of these people’s days ARE not blessed (ok, so there are those who say that no matter what, you’re blessed–tell that to the people who just got diagnosed with cancer).
I have found that I say “no problem” to “thank you” a lot, and this is bugging me, so I’m working on changing it. I’ve never heard “uh huh” in response to thanks, though.
I can see a company saying “thank you for calling Target, we appreciate you”, although to say “we appreciate your business” would be better. To say, " I appreciate you" in conversation just sounds wrong on several levels.
Yeah, like bad touching. I wouldn’t say that to anyone with whom I have not at least made out.
But speaking of inapproprite conversations, how often have you heard this one?
“Hi!”
“Pretty good.”
Or a phrase that my HS choir teacher used to use. Instead of saying “Quiet down”, he would replace it with “I can’t hear!” But he was polite about it, so he always said “I can’t hear, please!”
<Heath Ledger> “I don’ know how tuh 'ppreciate you.” </hl>
I’m fond of “peace be with you”. I don’t see how that could offend anybody.
Try saying that to a soldier about to go into combat.
“Yep, I’ve got my piece.”