The second problem is that the railway line to Gdansk is being upgraded at the moment so the journey takes about two hours longer than it used to and pretty much every single train is late too.
While I haven't been to Poznan yet, I just came home to the states from visiting Gdansk/Sopot a few days ago. My girlfriend and I had a wonderful time sightseeing both cities. I'll try to post some pics later. The weather held up nicely while we were there so my girl and I were able a couple of days on the beach too. I would definitely put Gdansk/Sopot/Gdynia on your destination list.
Unfortunately, traveling from Warsaw to Gdansk and back by train was a nightmare. We left Warsaw early last Sunday morning and it took us close to 6 hours to get to Gdasnk. Like Harry said, they were doing track work all along the route which slows the trip considerably. Our trip back to Warsaw (that Wednesday) was even worst. It had rained heavily that morning and I guess there was flooding along the tracks. We were supposed to take the 3:40pm train out but they had shut down the trains and the railway people did not know when they would be running again. My girlfriend and I were stuck at the train station and thought we would have to spend an extra night in Gdansk. Well after a 2 hour delay the trains were running again. But there were long, frequent stops all the way back to Warsaw. I even took a picture at one especially long stop (over an hour) of the railroad signals which were red most of time. So after all this, we didn't get back to Warsaw until after midnight. A very long, exhaustive trip home indeed.