Virtual Table Tops

[Senkusha]

I'm looking at options for VTTs.  I know of Roll20, and there are a few others, but what do you think of them?  Are there any features that you feel are missing?  How well do these work using a mobile phone (since most of my role playing time would probably be spent on the Bus or Subway).

Do you use online maps and tokens, or are your sessions mostly imaginative based?  I'm curious to know what your experiences have been using VTTs, since the only online experiences I have had involve using forums like this one.  Speaking of using forums, are there any items that could be implemented that would improve your playing experience here?