Most TAB lacks time signature and time value of each note. So if you don't know what the song sounds like you have no idea how much time to allocate to each note. The programs mentioned here are good because they overcome this problem.
Some of the problems that I have had in early on with reading TAB is that I saw TAB as just a string of notes. Until I realized that the notes were either chords or partial chords. Of course the full chord is easy to recognize.. sometimes partial chords are not as easy. I will sit down with the TAB and figure out what chords are being represented and pencil them in over the TAB. This way instead of just a string of notes, that I have to remember it becomes chords and chord shapes which I find much easier.