The sport button makes a noticeable difference to the forward momentum of the Zafira, it becomes nice with it on. I used it to get out of wycombe the other weekend, made it much faster! Then back off when I got on the motorway.
I drove 1.8 Astra SRis with it on and compared to my 1.8 Design which didn't have it, it just seemed like the same performance but I didn't need to give it as much of a shoeing, but if I drove mine flat out absolutely booting it I could replicate the effect of the sport button, in short I got the same out of both cars but with Sport button on I could just drive it normally/gently and it was like I was punching it, so I suppose it was good in that way that it didn't get tiresome or didn't get fed up horsing it, got the same performance for half the effort. It's not like the sport button being on makes it any quicker 0-60 or increases top speed or ups the BHP or anything, well not from standard anyway, I do recall owners of the 1.9 CDTI 150bhp cars with it remapped to 200+HBO trying to make the extra performance only available with the Sport button on, no idea how it turned out.