There's already a feature request pending to add some symbol beside the reputation text in each post to signify if you have repped that user yet. I think that'd be more helpful as you can instantly know if you've repped an user or not right on the post which made you want to rep them.
Quote:To know yet to think that one does not know is best; Not to know yet to think that one knows will lead to difficulty.
- Lau Tzu
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