It all depends on your machine and how much memory it has. The issue with Flash and MP3 streams is that Adobe has no concept of streaming this type of content...the available players just fill a buffer as if it was playing one large MP3 file. There are some tricks to try and get around this, but they don't work very well.
If you want to listen longer than an hour the best approach is to use Winamp (Windows) or iTunes (Windows/Mac). There are several other solutions, of course. Anything that plays MP3 streams.
Dave