Hi Bridgeland,
Although most of the time I have done delivery of the postcards through the post I have also been in the situtation were the only thing I could do was to hand delivery them. I got a few responses that way as well. (This is from another business) Since you are marketing to businesses it may be even better to hand deliver the postcard and have some face to face time with the potenial clients. In the past when I wanted to get clents for my business I went to some extreme as well and I would bake cookies wrap them up in a pretty package and attach my flyer or postcard to it with a bow and hand deliver that. That gave me the best results. Hope this helps some! Good Luck.