Is there a feature for member-to-member messaging outside of the "chat" area? I would like to ask questions of clarification to an individual user, but I can't remember where I saw the comment that I want to clarify to respond directly to it.
Private messaging is not available on the Stack Exchange network. To contact a particular user, you can (since you have the prerequisite reputation amount) do either of the following:
Find the user in a chat room and talk to them there. To find out if a user is in a chat room, search for them.
Create a chat room and then, using the same method as above to find the user, invite them to your room.
Your particular problem can be solved, as RegDwight points out, by using the comments sub-tab of the user activity tab, on the user's page. Once there, use your browser's text search facility to find the text you are looking for.