In the Russian internet community there is a subculture of net trolls called the Kaschenites (after Kaschenko clinic, a prominent Moscow mental hospital). Their favourite tool of the trade is Gratuitous Yiddish (and sometimes Gratuitous Hebrew), which tends to confuse the general population. The confused responses are then purposefully misinterpreted as antisemitism, which is then used as rationale for a flame war or simply to derail any given discussion.
Trolling aside, Russian in general experienced a huge Yiddish influence, especially southern dialects, which formed inside the Pale. Jews also were very significant in Russian culture and entertainment, so Yiddish never was all that foreign to Russians. Modern Russian exhibits level of Yiddish influence similar to New York English, especially in informal speech and slang.
And, in a funny aside, a lot of words that Americans perceive as intrinsically Yiddish, are actually Russian (or Polish), as eastern Yiddish dialects for their part also experienced an enormous influence of the local Slavic languages.
Yiddish and German are closely related: Yiddish began as a sort of Middle High German creole, so it's unsurprising that some words have filtered back, such as "meschugge", "Schickse", "Schlamassel," "Mischpoche", "Ganove" and a lot of others. All in all, there are estimated to be well over a thousand, many of them in constant use across all social strata.
Quite a bit of Yiddish vocabulary (along with a handful of Romani words) passed into everyday German via Rotwelsch, the argot of small criminals, beggars and vagrants (which also influenced the language of wandering journeymen craftsmen). Yiddish also preserves a few features that fell into disuse in Modern High German, such as the word "Tate" (two syllables) for "father". One also has to wonder if the use of at least some German words in Yiddish in American English (e. g. "bagel", "kibitz", "kugel", "schmaltz", and "schnorrer", or "Beugel", "Kiebitz", "Kugel", "Schmalz", and "Schnorrer" in modern German) may not have been reinforced by the presence of large numbers of German-Americans. Usages in German and American English can differ quite markedly - in the US, "schmuck" is seen as semi-obscene, while its German version, "Schmock", is harmless and is sometimes used in the meaning "snob".note The German word "Schmuck" means "jewelry" or "ornament."
New York Senator Al D'Amato is widely believed to have lost his Senate seat because he, as Toby Ziegler might put it, "brought the Yiddish without knowing what he was doing." In the closing days of a tight race against then-Congressman Charles Schumer, D'amato publicly referred to the Jewish Schumer as a "putzhead," without apparently being aware of what the word "putz" means in Yiddish. note "penis," with similar connotations to "prick." The resultant furor alienated the state's large Jewish community, which had previously been very supportive of him, and he lost by a ten-point margin.
African-American Colin Powell (former Chairman of the Joint Chiefs of Staff, Secretary of State) grew up in the Bronx and picked up Yiddish while working for Jewish employers.
Being that Yiddish, and not Hebrew was the everyday language of Ashkenazi Jews people for centuries, a lot of young Jews in America are learning it again in order to connect to their history.
The article Lawsuit, Shmawsuit studies the use of Yiddish in U.S. court decisions. The extent of usage should surprise nobody; the stereotype that all Jews are lawyers is, well, a stereotype, but it is not a stereotype that there are more Jewish folks at the American bar than you might expect based on their population alone, and thus it shouldn't be surprising that the American bench has a lot of Jews, too. As for the paper, one of its two authors, federal Judge Alex Kozinski (of the Court of Appeals for the 9th Circuit), is noted for the effective use of Yiddish in the Sophisticated as Hell style of his opinions from the bench (his most famous opinion is probably his opinion in ''Mattel v. MCA Records, in which the manufacturer of Barbie sued Aqua's record label over "Barbie Girl" and he "advise[d] the parties to chill."
Hacker parlance is absolutely full of Yiddish, as well as various other languages. See the Jargon File for examples.