My husband and I, and another couple, stayed in this apartment 18-22 September 2010 and really enjoyed it. =)
I've stayed at both the Parliament Sq. 1 and the Parliament Sq. 2 apartments, and though Parliament Sq. 1 has better views, I think Parliament Sq. 2 wins the contest for favorites with its amazing bathroom, its open floor plan, and its clean/contemporary feeling.
We enjoyed shopping the local markets for food to prepare in the apartment kitchen. The kitchen was great. Very spacious and well outfitted for cooking.
The location is, of course, fantastic! Very easy walk to Edinburgh Castle and right across the square from St. Giles. When we left Edinburgh, we just walked to the train station to catch our train - no problem.
Despite the fantastic location right on the Royal Mile, we didn't experience any problems with street noise. There are some ghost tours that run through the alley alongside the building in the evening, so you do get a little talking/laughing pedestrian noise there. But those tours didn't seem to run very late, and the apartment was altogether surprisingly quiet. If you're a light sleeper, you'll be happy to know that both Parliament Sq. 1 and Parliament Sq. 2 have wooden shutters and heavy drapes in the bedrooms to help cancel any noise.
I'd recommend this place for couples, families, a group of friends, mature travelers (as long as everyone in the group can handle the stairs - there's no elevator), or anyone looking for a spacious, relaxing, home-away-from home, sightseeing holiday apartment.