Not long ago I was talking to someone about going green and they actually told me that they had gone through 30 different tubes of caulking. They used it to plug the gaps and holes that were through their home. They put the caulking around the cracks, around doors, windows, and more. While I'm not sure how the job was that they did, since they used quite a bit of caulking, more than likely using the 30 tubes of the caulking actually do quite a bit of good. No doubt it helped them keep the home comfortable while saving money by increasing the energy efficiency of the home.
There have been times when I've been working on homes that had huge leakage areas. After having energy audits done it came out to several meters or area that were leaking, which is just as bad as having a huge window that is always open, even during the winter months. More than likely you wouldn't keep your windows open in the winter months, but many homeowners accidentally do things that are almost as bad because they have a lot of leakage areas.
For a nice tube of caulking, you'll only pay about $6, although ...