Our 5 days in Barcelona were great and Phil & Fiona's lovely flat was exactly as described - fantastic & central.
Phil & Fiona were great hosts from the start and communicated regularly - even helping to alter my booking when I messed my days up.
The flat itself is very centrally located and has everything that we needed for our family of 4.
There are some excellent restaurants and cafes right on the door step and all of the main tourist spots are with walking distance or within a short taxi/ metro ride. (Tip - we found that for 4 of us the taxi was actually cheaper than single metro rides, and much quicker)
Only two small niggles that we can think of - firstly the street outside is a bit noisy (especially when the downstairs restaurant empties the bottles at 11pm) so ear plugs are a must if you are a light sleeper and the apartment can get quite warm. Phil & Fiona do provide pretty heavy duty fans, which help a lot, but the inner bunk room was quite warm for the children.
That said we loved it and managed to cope with both of these niggles and they would not be enough to put us off staying here again if we come to Barcelona.