A great piece by Craig Gilbert of the Milwaukee Journal Sentinel comparing the voter turnout in the different primary races. It should be noted that the turnout is (except in one case) for primaries, so you would expect it to be lower than for the general. However, the turnout is quite high for a recall. Gilbert makes a number of comparisons to Wisconsin (including the Gary George recall which had 8% turnout -- though Gilbert told me that it was in a low-turnout area).
In other states, we've seen recall turnout appear very low, including in the hotly contested Michigan recalls of 1983 and the California ones of 1994-5. It may be that the Wisconsin recalls are that special event --like the Gray Davis recall -- that could result in higher turnout than in a regular general election.