Simon Liebross has been my relative first in the United States. Early on I'd located an 1890 manifest for him and his wife Etel (Ethel). I was satisfied with that until I found the following index card for Simon's naturalization. 
Simon had become a citizen via application to the U.S. District Court in Brooklyn, New York. He finalized the process on 4 May 1899 (volume 14, record 281) when he lived at 71 Gerry Street in Brooklyn. He said he was a manufacturer, born 26 December 1863, a citizen of Austria and had arrived in the United States via the Port of New York.
All of of that information either matched or was quite close to what I'd already gleaned via other records. All was well until I noted the date of arrival: 13 August 1881 - nine years earlier than expected. I located the image of the original naturalization record. 
The index card transcription of the Simon Liebross' naturalization record was correct. I have annotated the section of interest on Simon's naturalization record with a white box. The selected detail image is pictured below.
While no ship was stated, I hoped that the date of arrival was accurate. It was.
I queried Ancestry's manifests by only putting in the date of arrival: 13 August 1881. There were more than 900 results, but I scrolled through to see if there might be any surnames resembling Liebross.
Ancestry's index listed passenger 620 as "H. L. Liebraefe." That looked promising. The manifest actually says, "Liebrosfe."  The letter f being the typical (of the time) manner of doubling the letter s. The second initial is definitely an L, as indexed. I am not sure, however, of the first initial.
In census records and his death record I have found a variety of ages and birth years for Simon ranging from about 1855 to 1863. So, the age (20) is also about correct for Simon. The manifest also indicates that Liebrofse is a male and his occupation is clerk. The S.S. Elbe took him from Bremen to New York's Castle Garden.
I have searched a variety of city directories and, thus far, cannot account for Simon's whereabouts between 1881 and his second manifest in 1890, when he returned accompanied by his wife. So, I do not know when he left the USA and how long he was back in Eastern Europe.
1. "New York Passenger Lists, 1820-1957," digital images, Ancestry.com
(http://www.ancestry.com: accessed 28 May 2008), manifest, Rhaetia, Hamburg via Le Havre to New York, arriving 25 January 1890, passenger number 188, Simon Libros; citing National Archives Microfilm Serial T237, Roll 543, line 35, list number 93.
2. "U.S. Naturalization Records Indexes, 1794-1995," digital images, Ancestry.com (http://www.ancestry.com : accessed 17 May 2008), index card for Simon Liebros (naturalization 4 May 1899), citing National Archives and Records Administration "Index to Naturalization Petitions of the United States District Court for the Eastern District of New York, 1865-1957, Microfilm Serial M1164, Microfilm Roll 10.
3. "Selected U.S. Naturalization Records - Original Documents, 1790-1974," digital images, Ancestry.com (http://www.ancestry.com : accessed 24 September 2010), Petition for Naturalization for Simon Liebros (4 May 1899), Volume 14, Page 281, citing National Archives and records Administration "Petitions for naturalization of the U.S. District Court for the Eastern District of New York, 186501837, NARA Series M1879.
4. "New York Passenger Lists, 1820-1957," digital images, Ancestry.com
(http://www.ancestry.com: accessed 29 August 2010), manifest, Elbe, Bremen to New York, arriving 13 August 1881, list 1119, passenger 620, indexed as H.L. Liebraefe [?. L. Liebrosfe]; citing National Archives Microfilm Publication M237, Roll 440, Records of the Customs Service, Record Group 36.