Are there Conference Proceedings that have impact factor? In Medicine, an Impact Factor of a journal is important indicator (IF) of journal quality.

Are there examples of conference proceedings that have a formal IF figure computed?
Are there examples of conference proceedings that have a formal IF figure computed?


There is nothing like the "formal IF". What you are referring to is probably the Thomson Reuter's Journal Citation Reports impact factor which is one of the most respected measures in the academic world. As such, to my best knowledge there is no such thing for conferences.

However, there are other sources which could prove useful as an estimate of conference quality:


As already Charles pointed out, there are exist cached versions of Citeseer's estimated impact factors for computer science, but this is too old to be useful. 
Furthermore, Google Scholar lists ranks of top venues mixing journals and conferences in their listings. Here is an example of top publications for AI, as you might see, there are several conferences mixed in. They list h-index of the venue instead of an impact factor. 
Another very useful, resource for ranking conferences is Microsoft Academic Search, where you can find profiles of conferences, such as this one for IJCAI and they also publish rankings for different categories of venues, see an example here. 
Finally, you might find useful the Australian Research Council's ERA conference rankings from 2010. In 2012 they decided not to rank conferences any more, but the 2010 list is still very useful and at least somewhat authoritative. They would rank conferences into categories according to their own quality metrics, which however (at least in my area) correlate with the community's perception.