In the anime, when the Pacifista was locking onto to Usopp for its next attack, its bounty detector labeled him as Sogeking, even though he was not wearing his Sogeking mask (though his nose or the Kabuto could have given him away).
Although it is a fact that the newspapers (2 years later) managed to recognize Usopp, as he was labeled "Sogeking", proving the Pacifistas have the capability to recognize him.
Usopp's name is probably based on "Isoppu", which is the Japanese pronunciation of Aesop, the ancient Greek fabulist. Considering that uso means "lie" in Japanese, the name Usopp can be taken as a portmanteau name between uso and Isopp, since Usopp is both a liar and a storyteller. The name is also a Japanese pun in that saying "Ore wa Usopp!" can mean either "I am Usopp!" or "I am a liar!" because Usopp's name is written using Katakana characters and not Kanji.
In regards to his alter-ego, Sogeking is a play on words as the Japanese word for sniper is "Sogeki".
In order to avoid references to death, Usopp's "Sure Kill" part in his attacks' names are removed in the 4Kids dub. Both Usopp and Yasopp were voiced by Jason Adam Griffith.
In addition to the Straw Hats' jolly roger, Usopp also has one of his own, like all the other members of the crew. The flag was first seen when Luffy asked him to design and paint a Jolly Roger for the crew. Though it was supposed to reflect everyone, Usopp designed his own jolly roger as their symbol, reflecting his delusions of captainship. It has Usopp's nose, bandanna, a star, and a slingshot for a cross-bone. Usopp's design was immediately rejected.
Usopp has a second personal jolly roger after the timeskip. In this version his skull is seen on its left side with Usopp's new hat, headphones, and his curly hair tied back. The Kuro Kabuto is seen on its side in the background.
Usopp can be seen in the corner of Luffy's former wanted poster and Zoro's former wanted poster. In Luffy's he is simply viewed from behind. In Zoro's his silhouette is faintly seen through the smoke in the background of the poster doing his Crocodile impersonation. However, in the anime, the latter was cut out of Zoro's poster most likely due to the fact that it is not easily visible and was thus overlooked. It was later corrected in Episode 152 but omitted again in the second bounty poster. It is unknown if he's seen on Luffy's and Zoro's actual wanted posters.
It is possible that Usopp's long nose was inspired by the fairy tale "Pinocchio", as Pinocchio was a wooden puppet whose nose grew longer whenever he told a lie.
Usopp's personality could also come from The Adventures of Baron of Münchausen, who said he had traveled around the globe on a cannonball, a lie Usopp himself said in episode 19, though no one gave any attention.
"The Boy Who Cried Wolf" is a story of a boy that often tells lies of an impending wolf attack in order to gain attention, much like Usopp lies of imminent pirate attacks. When the wolf actually did arrive, no one believed him. This story was written by an author known as Aesop. The word "uso" means "lie" in japanese. It is possible these two instances are the influence behind Usopp's name.
Ironically, most of the tall tales he told Kaya have came true at some point during the Straw Hats' voyage. These include meeting a giant goldfish (as the crew was leaving Little Garden) fighting against a giant mole (against Miss Merry Christmas during the climax in the Alabasta Arc), meeting dwarves (when Robin and Usopp were captured by dwarves in Green Bit) and being a captain (as he is called by all the toys and dwarfs when he frees them on Dressrosa)
Despite being the weakest crewmate (according to Oda) Usopp is the fourth crewmember to awaken Haki behind the Monster Trio.
He, Luffy, and Sanji claim to have never been sick, and thus do not know what it feels like.
However, on the SBS Volume 73, Oda stated that Usopp once fell sick after eating a poison mushroom.
Ironically despite being a coward Usopp has no fear of spiders as in seen in Jaya. Even picking up a tarantula and petting it while the usually much braver Sanji jump into bushes at the mere sight of the arachnid.
He is the one who introduced the rubber band to the Skypieans.
Kappei Yamaguchi, Usopp's Japanese voice actor, came up with the notes to the Sogeking song. Oda provided the words and then asked him to develop the notes himself. Kappei also stated that the Sogeking song is the most requested song for him.
Sonny Strait, the FUNimation voice actor for Usopp, has stated several times during the FUNimation DVD commentaries that Kappei Yamaguchi is his favorite Japanese voice actor, saying that whenever he listens to Kappei's performance in recording it is like he is saying "Top that American voice actor!".
In the 5th Japanese Fan Poll, Usopp was voted the thirteenth most popular character in One Piece.
Usopp's birthday is on April 1, which is April Fool's Day. This is quite fitting considering Usopp's ability to fool people.
Skypiea has a theme park dedicated to Usopp called "Rubber Band Land". It has a drawn profile of him on the overhead sign and a statue featuring him as a muscular warrior, complete with a spear. 
Usopp might be somewhat based on the Japanese mythical species tengu, who were said to have long noses and habits of tricking people. Kin'emon even referred to him as a tengu.