Corollary: The Russian Pale of Settlement isn't quite as big (if it exists at all), and some of my ancestors might have stayed over in that part of the world instead of coming to America in the early 20th century. The Tsarist government was pretty antisemitic, and both Russia and Prussia/Germany were anti-Polish. Austria Hungary was apparently a little bit better but they wanted to keep their empire together.
Because Poland-Lithuania stays independent in some form, this affects emigration patterns to the New World. Fewer eastern European immigrants, and fewer Jews leaving for the Levant, maybe. Perhaps people are happier in Poland than in OTL, but there might still be serfdom. However, Poland isn't immune to the outside world, and so we might see serf emancipation by the late 19th century at the latest.
Also, Germany is slower to evolve and strengthen because of a strong country other than Russia on its eastern flank. Russia will of course be strong anyhow (it has a ton of territory and sparsely populated expansion room, so Russia or some other big state to the east seems pretty likely). My guess is that Russia and Poland would fight some wars against each other by the early 20th century at the latest, and there might even have been Polish designs to keep Germany divided or weak. Anyone up for a Polish/French/Italian partition of Germany? (other than mid-20th-century, which is a bit too close to OTL*, anyhow).
*Ok, Russia, France, England, and America, whatever. But that was a different grouping, more Western-democratic-socialist in nature, and thus led to a different dynamic. Poland/France/Italy in the 19th century (or Poland/France/Ottoman Turkey or Poland/France/Austria for that matter) would've been more monarchic or authoritarian, I suppose (France had some pretty wild swings of political structure in the 19th century, though).