Once of heard of this tool and the fact that in worked with Query analyzer and Ultra Edit made me want to try it out. But like many of the other responses, I found the tool to be rather buggy.
First the fact that the prompts work some of the time but not all of the time is rather annoying.
Also, when I prefix a table then begin typing in the "where" clause, SQL Prompt will bring up a list of all the columns rather then waiting until I enter the prefix. Once you press the dot it inserts the column that started with the same letter as the prefix (unless you type fast then it simply inserts the first column in the list). For example instead of "select * from TableA a where a.<list of columns>" I get "select * from TableA a where aColumn".
I've seen the performance hit mentioned before but after a few seconds it seemed to get better. Hopefully this will be improved in the next release.
So in the end not much time is safed by using this version because I must constantly undo and retype or check that not only if the prompt comes up but if it displaying the correct information. Maybe I didn't have it configured right but then again I really didn't want to spend a lot of time tweeking the tool just to get it to work correctly for a basic query.
I think the idea is great and will definitly revisit this when 3.0 is released, but even free is too much for me for the current version.