You may attract some looks, but generally that's about it. And those looks won't be because people have something against you, just we don't see that many black folks here (the smaller the city you wanna visit, the more looks you'll attract. But those will curious looks, more often than anything else).
Any safety advices I may give you here, are something common for people of all colours and genders when they travel alone to a different country not knowing the language. Elder Poles, don't speak English at all. You might have to get use to a lot of pointing at things in shops and so on - but younger generations are taught English in schools, so with high probability you'll be able to communicate with them.
Beside that? Avoid walking streets alone after dark, don't drink with people you don't know and don't eat the yellow snow ;)
Speaking of snow - if you plan visiting during cold season (that is since November till March-ish) be ready for temperatures below 0 ºC/32 ºF
Poles are generally friendly folk. Arm yourself with a dictionary or at least a map and you're good.
Hmm.. what else...? Depends what part of Poland you want to visit, what part of culture or history you're interested in? A weekend isn't much time to get even basics of all those things covered - so it's even harder for me to give you any overview of it here.
In any case, have a fun trip (if you thinking about visiting Warsaw might try to give you some "must-see-in-2-days" list of things)! :)
..:: EDIT ::..
Warsaw is most cosmopolitan city in Poland, to my knowledge - I see black people pretty much everyday in downtown. Standing, sitting and waiting on our public communication alongside everyone else. Hell, we have a black member in the Parliament - http://en.wikipedia.org/wiki/John_Godson
So yeah, visiting Warsaw you must be ready for some public transportation issues. There's just one line of metro here - they're building 2nd one, but it will be few years so...
If you're not planning to use TAXI, buy a 3-day City Travelcard - should be available in most news-stands. Once you have it, enter bus, tram or metro and validate it in the validator thingy - and you're good for 72 hours. To move effectively (who am I kidding..) around city check out http://www.ztm.waw.pl/?l=2 route planner.
Things that are "must see" in Warsaw depend on what you want to focus on. Due to Polish history there is a lot of places, museums and expositions related to WW2 - from which most prominent is:
Warsaw Uprising Museum - http://www.1944.pl/en/
It focuses not only on uprising itself, but on lifestyle of normal people under nazi occupation and during the uprising.
National Museum - http://www.mnw.art.pl/index.php/en/
National has revolving doors policy with the temporal exhibitions, but part of the permanent exposition is the "Polish Art Gallery" and "Polish 20th-century Art Gallery" (if you wanna focus on Poland only)
Royal Palace - http://www.zamek-krolewski.pl/?page=1114
RP's exhibitions are most often related to Polish history, with focus on Warsaw in particular.
It's also common to look at Warsaw from 30th floor of Palace of Culture and Science... I wish I could give you some links to PoCaS but... they don't have English version of their page so... ;) Building itself can't be missed, it's that strange looking thing in middle of downtown, tall, grey and with clock on the top that you can't see most of the time anyway ;)
Last of the big things imo, even if little remote is Wilanow - http://www.wilanow-palac.pl/
Palace build for John III Sobieski in XVII c. gathered rather impressive collection of art over the years.