tweaks that impress the unsuspecting

What I'm interested in are tweaks that impressed friends or significant others WITHOUT being told beforehand that the tweak was done...If they were tipped off first, it doesn't count.
None - the most impressive thing in recent years was Planet Earth on HD 1080p. This bowled over unsuspecting others. No minor audio tweak has ever impressed unsuspecting others. Our unsuspecting dogs go ballistic on test CD's with just talking - they think an intruder is in the house - TV or radio never does this.
One of the best tweeks bar none was the addition of an Auralex "SubDude" isolation platform for my sub. Best $50 ever spent on audio. Unbelieveable, kills any unwanted vibrations and resonances that muddy the sound.
I second Oddiofyl's observation re SubDude. With my Velodyne HGS-15 and HGS-10 the SubDudes removed the boom and extended the bass.