If you are wondering why Maya seems familiar it is because you've seen him in both World Baseball Classics pitching for the Cuban entry. He was one of the best pitchers in Cuba before defecting last September. He was the ace of the Cuban rotation that included Aroldis Chapman. he won the Cuban equivalent of the Cy Young in the 2008-09 season. Most scouts believe he can pitch for the Nationals almost as soon as he arrives.
Fantasy owners should be very aware of Maya. He may even impact the pennant races in some leagues, especially NL-only leagues. He'll report to Florida for extended Spring Training but should move through the system quickly.
EDIT: To add quotes from the August 1st Press Conference (h/t FederalBaseball.com)
"The actual negotiations went fairly quickly once were able to negotiate," DC GM Mike Rizzo explained when asked how long the team had been talking to Maya, "There's a strict policy and the red tape of getting him the documentation he needs to come to the states....we went after him quickly and aggressively as a person we thought could give us instant impact at the major league level for the long term and that's the reason we decided to sign him to a major league contract." (ed. note - "According to Washington Post writer Adam Kilgore, the contract is worth $6M over 4 years.")
The Nationals had a "very thorough evaluatory process" of the pitcher, Mr. Rizzo continued, "He was seen I think by five separate scouts on separate occasions, during international competition over the years, most recently during the World Baseball Classic and we had multiple reports on him and we scouted him very in-depth in the Dominican Republic once we got over there."
"How soon will Maya be in the Majors?" Mr. Rizzo said that, "Yunesky's going to be around [in D.C.] for a couple days to see the ballgame(s), then he's going to immediately fly to Viera [FL] to throw in front of our Pitching Coordinator Spin Williams. We're going to assess where he's at in his conditioning and how stretched out he is as far as a number of pitches he can [throw], then...he'll throw a live bullpen, a simulated game, do a rehab start, then we'll reassess at that point where he goes, if he comes directly to the big leagues or to the minor leagues for a little bit of more seasoning and to build his pitch count up."