Balance shafts were only used for NVH reasons, certainly not for performance (why add the additional rotating mass).
From what I recall, balance shafts were only used in bigger 4cyl motors. Smaller displacment 4cyl don't have as long a stroke (thus causing not as large a side-to-side vibration - at least as I understand it). I believe that motors with 2.0+ litres were typically good candidates. Its been awhile since I checked it out, but I think Porsche (for 944s/968s, remember 3.0l 4cyl
), Honda (2.4litre in the older Accords...my memory?), and as as EricSC has already mentioned...some Mitsu's. Not everyone did this because not everyone had bigger 4cyl engines or chose not to do the R&D. I'm sure there are also a myramid of other reasons why manufacturers decided (or not) to go with balance shafts.
Thinking out loud..
Positives: Less NVH, others??
Negatives: Added rotational mass, additional wearing parts, expensive R&D, expensive to manufacture, etc., etc. etc.
I believe they are hardly used anymore because if NVH is a big factor for your target market group, they likely go with something like liquid filled engines mounts these days (read=much cheaper).
I would be surprised if someone is still making them.
[This message has been edited by markus (edited October 03, 2000).]