Lifehacker.com (Australia) offers readers the following tip using vinegar to remove stickers:
Use a paintbrush or paper towel to paint the area lightly (very lightly, in the case of a laptop or something sensitive) with vinegar until it soaks through the sticker or gets in around the sides. Let the vinegar set for a five minutes or so, and then wipe the excess vinegar away and try to peel or scrape the sticker away.