I was approaching Markarth on my horse and an NPC comes to me and just stare point blank at my horse. I had to get down to find out that he was a courier. Beth, please if not give us horseback fight at last make NPC initiated dialogues to start while you are on horse. But this is a minor annoiance, the best is to come...
So, this courier says he has something just for my eyes then a message in the top left corner sayse "One item(s) added" (or something like that, i don't have the game near but "ITEM" not something esle). Now guess what was that item? as Beth considered it funny to make me search for it. I had to go and compare inventory with previous save game.
It was...

Not an issue at all. Don't you know it's proper etiquette in Skyrim to dismount your horse before speaking to others?

So you didn't figure out the courier gave you a letter? IIRC, that's the only thing he can ever give you.

Just keep your inventory clean, stash all the letters and notes in your house or throw them away once you're done with the associated quest and you won't have a problem like this again.

Which is why I always kill the wealthy guy on the horse.

Actualy I went for the stright to the books section, but I have a few jurnals and notes there and stuff like that which I don't remember if they were of any use till now and don't know if they will ever be so I keep them especialy those with 0 weight. But you may be right they will never be and I can just store them as I could store this letter just away...anyway you realy don't see any issue with that message when there is clearly posible to have there the exact name of the object received as in most other cases.

Yes, I think it should be "You received a letter" or something, but then it would still be one new letter among dozens of other letters you kept in your inventory

With me, it's been more of a case of "who is this idiot attacking those bears?", get off horse, kill bears, search guy's body, "well, waddayaknow, a letter for me, what are the chances?"

Horses are poorly implemented. I remember that after the first teaser they said that they weren't sure if they would include horses. They would only do it if they could 'get it right'. I don't use them so I don't care that they are in the game, but based on what they said about it I think they shouldn't have added them. Perhaps they can get someone from Rockstar to do work on animations for future TES games.

Yeah this happened to me to, it's strange.

I hope it will be patched soon.