Warsaw is the only city in Poland where I recommend to use guarded parking lots. Why? Well, maybe I am wrong now. I've seen motorcycles from the Netherlands with luggage outside parked on a street by the Uprising Museum and there are thousands cars (including the very expensive ones) parked along streets by locals, but read please my Tourist Trap tip "Car thefts and burglaries." There are many guarded parking lots in downtown/centre and around compact old town which is mostly closed for traffic, look for the writing PARKING STRZEZONY (map here). Check here - I once used that underground one called Centrum Jasna at ul. Jasna 14/16a and here. Most hotels (even the fancy ones) don't have own guarded parking lots but there is always one closeby (usually underground). Expect to pay some 7 - 15 euros per 24 h.
If you decide to park on a street keep in mind that the whole center, the old town (mostly closed for traffic) and some other parts of the city are zones of paid parking (strefa platnego parkowania - SPP) on business days from 8 am until 6 pm (map here). These streets are usually (but NOT always) marked by signs P (parking) with PLATNY (paid). Look for blue-grey or brown parkometers, large machines which don't give any change and are unfriendly for those who can't speak Polish. Put coins until you see required end time of parking displayed on the screen then press AKCEPTUJ (accept) and take a ticket, otherwise press ANULUJ (cancel). Put the ticket behind widscreen on driver's place! There are chip parking cards available in kiosks. Put it into a slot in a parkometer and press + to add time. The parking in SPP costs per hour: 1st - 2.40; 2nd - 2.60; 3rd - 2.80, each next - 2.00 zl and didn't change in 2003 - 2006. That's 17.8 zl (4.7 euros per day).
Warsaw, like many former Soviet bloc countries, has seen a large increase in traffic as the standard of living rises. Auto traffic in Warsaw during weekdays is VERY heavy. I would advise taking public transit rather than use a rental car if you can do so. It is much cheaper and very easy to use.
Parking, as in most European cities, is at a premium and expensive. I strongly urge to use the public transit in Warsaw if you can. It seems safe, is well-kept and modern. I rather enjoyed using it while I visited there.
If you love driving in rush hours in Paris, Florence or Rome you may try to drive a car in Warsaw otherwise leave your car on a guarded parking (read my next tip), walk and use public transportation or taxis. Why? Do you want the whole list? OK, just top 6:
1. Heavy traffic jams from 7.00 am to 7.00 pm on business days and on weekends (Sat morning from the city and Sun evening to the city). It took me 4 hours to pass through Warsaw on the way back from Lithuania. It's the only European capital (except Tirana, Albania) which still don't have any ring road/beltway and no freeway/motorway. All traffic goes through the city! And keep in mind that some 60% adult Poles do not work, they seem to drive all the time ---> no specific rush hours in Warsaw.
2. Local drivers always try to drive too fast and love to change lanes unexpectedly. Well, some are kind :-) but some rude and aggressive... There are numerous fatal car accidents in Warsaw. In January, 2006, five pedestrians were killed on a bridge hit by a driver who drove over 100 km/h instead of 50 km/h... on a snow! Craziness!
3. Roads/streets are poorly (hidden, small signs, strange, small destinations on direction signs etc.) sometimes WRONGLY signed (try to drive from Katowice to Bialystok or back!) which I can't understand, no responsibility in the City Palace...
4. Some unwise pedestrians (old ladies and young boys) try to cross a street everywhere... never mind the fast car traffic.
5. Shortage of parking place on streets, car thefts and burglaries (read my tourist trap tip).
6. Accceptable alcohol blood level for a driver is only 0,2 mg%, forget about even one beer.
All the roads lead to Warsaw (apart the sea roads). However you can reach Warsaw by the ship sailing through the Visula river. But it is a journey for people with fantasy. The Okêcie Airport serve a few millions of passengers a year, railway stations are always full, roads leading to Poland are crowded. Warsaw is one of the most frequent visited cities in Europe. Thanks to its great location, many foreign companies built their offices there. It is the most expanding city in Europe, after Berlin. Businessmen mostly flight to Warsaw. It is seen at the streets. In the rush hour Warsaw is like Tokio or Paris. Traffic jam is horrible. So, it is better to use a public transport, especially trams or subway. Warsaw taxis are also comfortable. There are lots of taxi corporations in the capital of Poland. They vie witch each other for clients, and passengers like it. In the crowded public transport pickpockets take profits. So you must be careful. For romantic travellers we propose a Warsaw cab. It is a great occasion to talk to cabman, who saw and heard a lot.
what is unique about the highway traffic in poland is that all the highways accross the poland are going through the very center of warszawa! and your way out of the city has extremely poor directions.