Good point. I used them a couple of years ago, until I got into a pay site that I prefer.
isc though is quite amazing in that it's live, real time, and the people that play on there are something else again. Your games are timed. The real scrabble freaks will play games with a 3 min. time limit to defeat the use of "word generators" Very adrenaline-soaked crowd. The system allows you to replay each move, with your and your opponent's tiles in different colors, with the time on the clock showing, down to the 1/10th of a second (not that you really need that). Never had a problem with the site (that I know of).
Oh yeah, no adware. Pay sites are a better bet generally (that's what I use), but isc is unique and impressive.