have about 72 hours burn in. mids still sound like crap compared to my lcd-2. they didn't blow me away at all like the set that the distributor allowed me to demo with at my house. same set up. thankfully they've agreed to provide me with another set to A/B when the next shipment arrives.
with music that doesn't have vocals on them it's less noticeable, but it's undeniable with music with vocals. my lcd-2s, which I had with me for half a year, sounded way lusher in vocals. unlike you, i'm refusing to believe i hear any improvement from inception.
do let me know how your lcd-3s progress as well!