It's my understanding that one could comfortably take a day trip from Krakow to Warsaw by train. Based on my reading of the schedules it looks as though one could comfortably do half a day in Warsaw with an under three hour train trip in each direction.

Is this assumption correct and are the trains reliable enough to make it worth doing?

Thanks,
BigBlue

looking at Official Polish Train Site http://www.pkp.pl/english/rozklad_eng.php
You should have no problem do do a day trip to Warsaw - with train to and from Warsaw almost around the clock leaving every hour or so (with 2/3hrs intervals during a night time).
Most are direct with around 2hr and 40 min. of travel leaving early from Krakow and bit late from Warsaw - would give you a good day in Warsaw.

Buy Roundtrip ticket in Krakow - so you would not need to advertise your wallet contents late in Warsaw Train Station...

Virtual Warsaw -> http://um.warszawa.pl/v_syrenka/miasto/unesco.htm
Major attractions in Warsaw ->http://www.e-warsaw.pl/miasto/atrakcje.htm
http://www.e-warsaw.pl/miasto/turystyka.htm

Peter, thanks for your input and website references. The frequency of train service and the duration of the trip aren't my concern. What is of interest to me is how reliable the trains are. Do you have any experience in that regard, please?

Thanks,
BigBlue

The train service between Warszawa and Krakow is usually on schedule and on time. This is an important route for PKP. Start early and leave late!

Most trains are reliable esspecailly between major cities - there maybe some small delays from time to time but really not too much concern when you have no changes - delays also do happen do to weather (excessive snow etc.) but only very few heat their tracks in the world so I guess that could happen really anywhere...

Safety in trains is another issue - when trveling in late hours or really anytime - find other travelers so you are not alone ... and just watch your stuff and pockets (esspecailly when boarding)...