We stayed in Ta Som Guesthouse for 3 nights (November 26-28, 2011). We were picked up by the tuk-tuk from Mekong Express bus terminal (included in the package). Upon arrival, we were served with banana shakes and cold towels. Our room was spacious and clean.
PROS: They have several breakfast options (all served with coffee or tea and fruits); Caltex is just beside the guesthouse; Angkor Archaeological Park is just 10 minutes away; free tuk-tuk ride to Pub Street (5 minutes away | 10-15 minutes by foot); soap and shampoo were provided; being a Capitol tour branch office, I was also able to book us bus seats to Bangkok; souvenir :D
CONS (minor): It takes some time for the aircon to cool the room; the TV has limited English channels; the room only has a 'makeshift' cabinet; I don't know why but the beds were too high; towels were not changed daily (I think you have to request for it)
If you're looking for cheap but comfortable place to stay in Siem Reap, you might want to consider Ta Som Guesthouse.
More of my review here: http://www.excursionista.net/2012/01/exploring-indochina-ta-som-guesthouse.htmlMore