Spent one weekend there. Was either freezing my ass off, or hanging out the back of a local girl. Worth traveling up the top of the big tower donated by uncle Stalin. Krakow is a much nicer city btw..
Krakow is a more picturesque city, it has to be said, but it is a tiny bit up itself compared to Warsaw, according to my Polish missus. I was in Warsaw last weekend, actually, supporting my girl and her brother running in the Warsaw 10K race. I really like it though I've only been there two or three times. The aforementioned Palace of Science and Culture is well worth seeing (and it has some funky bars inside it). In front of it right now are a series of statues to celebrate the Euros. The England statue has a "Free [Poor language removed] Riot" slogan on it, which I though was ace.
The Nazis' final act, on retreating from the advancing Russian forces, was to level the city (over 70% of the city's buildings were destroyed) in vicious retribution for the courageous but ultimately foolhardy Warsaw Uprising of 1944. With typical bloody-mindedness to Poles consulted old Canaletto paintings, various sketches and any surviving town plans and rebuilt the old town, brick for brick. It might look hundreds of years old but it is in fact less than half a century old. I love that. Possibly the biggest "[Poor language removed] you!" in European history.
With this in mind, The Museum of the Warsaw Uprising is well worth seeing (if a bit jingoistic).
Don't bother looking for the Ghetto, it's now the financial quarter and mostly a collection of highrise glass banks and hotels.
I don't really know the names of any bars but just have a nose around (or better still, buy a Lonely Planet guide). The Poles are generally very polite and helpful, in spite of what Nik says.
Have fun.