Part of the problem is good estimates take time. For many things you can't give a good estimate after 10 minutes of analysis much less the 10 seconds some people ask for.

Because of this I offer two estimates: one that might be off by a factor of 100x, and those that are fairly accurate but take more time to make. My boss usually goes for the former.

Edit: also there's two types of estimates. One measures how much of my time it will take. The other measures the date it will be done and/or live. The two are oftentimes different numbers, and as a developer I can't always control the 2nd.