No. It never occurs to me to use the MSC when searching, and I don't know why I'd want to use it rather than search for specific terms.
When I have to list MSC codes for my own publications, I often find that they don't seem to fit very well. I'm sure I couldn't design a better classification, but as a search tool it seems to me to have outlived its usefulness. Maybe there are other uses.
(For comparison, which is better: a system where you type "guacamole recipe" into a search engine, or a system where you first learn that 381798.45 is the Thing Subject Code for "Mexican food", then browse the list of all web pages with code 381798.45?)