I've been a fan of the house-ruled abstract encumbrance system that Lamentations of the Flame Princess uses since I first read about it on Telecanter's blog. The one thing that didn't sit right with me was what to do with stronger characters, who quite reasonably wouldn't feel the burden as much as their weaker comrades-in-arms.
A simple solution is to subtract two slots worth of encumbering items per point of strength over 12. That way, a character with 18 STR could go from say, 19 slots (3 Encumbrance, or "Heavily Encumbered") to 7 slots (1 Encumbrance, or "Unencumbered"). Items would still be recorded, of course. Tying it to every point of STR makes a 13 or a 14 really worth something, as it might just be the difference between Heavy and Light Encumbrance.