how many points is it possible to score in spider solitaire intermediate?

You can get as high a score as you want.  It just takes time.

Find a game where when you clear a column you get the no more moves screen.  You just got 100 points. Click to return to the game and undo.  The game forgets to take away the 100 points.   clear the column again and get another 100 points (minus the point for the undo and the point for the move to clear the column).  Wash, rinse, repeat until you reach the score you want or get bored.

My highest scores for Spider Solitaire (Windows 7's version) on intermediate are as follows:

1238 (5/23/2010)

1222 (6/20/2010)

1214 (8/30/2010)

1195 (4/4/2011)

1180 (6/12/2011)

I'm positive there are higher scores possible. :)

Wikipedia states that the highest possible score is 1293 given a perfect deal (and I'm assuming that's on Expert mode given the additional score possibilites being lower than what I've achieved on intermediate mode).

Win percentage is almost meaningless (addressing another "answer") as all games of Spider Solitaire are winnable given the unlimited undo's in Windows' version. I've played 646 games thus far with a 100% win percentage.

Wikipedia link: http://en.wikipedia.org/wiki/Spider_Solitaire_(Windows)#Highest_Possible_Scores