I will hardcode a magic number in the code and mark it with an comment next to it like "# XXX should be in config file".
I do it because I want to stay in the flow of programming and feel it will be easy to return later for the brain dead task of moving the number out to a config file instead.
If I knew the number would need to appear multiple times throughout a code base, I'd probably go ahead and add it to a config file immediately.
As part of my refinement process, I'll grep the code for XXX comments to see if anything has been flagged for later attention.