I've never had a problem with pimples--in fact, I think I have pretty nice skin, even at 33. When I was younger, I never even washed my face, which I shudder to admit now, apart from a splash with water and rub with my fingers when in the shower and a little make-up remover.
When I turned 30, I started on a full-scale skin regimen, which included trying Biore strips. I didn't use them very often, but got some little columns when I did--mostly on the right side of my chin. After reading reviews here, I tried the use-after-shower method (I also always wash my face right before applying the strips, as directed). This method got out a considerable amount more (including a little on the left side of my chin, which never leaves anything on the strip). I'm not sure of the effect of the strips on acne, but I do notice my pores are absolutely invisible after using these--which I do now once a week. I love them, even if just for the satisfaction of knowing that stuff is no longer in my face.
While I can't say if these strips have any effect on blackheads or acne, I can say that they remove even thin white columns that otherwise have had no visible effect on my face except to enlarge my pores a little upon careful close-up inspection. However, I use them every week and will continue to do so.
Yes, they're a little pricey. However, I buy them in bulk when I find them on sale somewhere. If you hunt around, you'll be able to find lower prices. Since I only use them once a week, they last for quite some time.