I know I know, old debate, I just decided I'd share my experience.
So I just came across a grey label 1391401 from '88 and after cleaning it up tonight, I started to type on it.
Right away I noticed a difference. Since I have been typing on my Minitouch(white alps) I thought maybe that was just me getting used to BS again after a while away. Then I got out my other 'board, blue label 1391401 from '93 and tried them side-by-side.
There is a major difference in feel between the two. The grey label feels much lighter and less kerchunky than the blue label. I did a few more side-by-sides and what I ended up finding out is that the grey is not actually lighter, it is heavier!
The thing with the blue is that it seems a little bit smoother so that when it actuates it's much more noticeable. I used my official Rip-O-Meter to test the two and the blue came out at 65g consistently and the grey label came out at 70g consistently.
I thought this might be a spring-wear problem, but trying all the keys on the blue, including Scroll lock, pause and the like they were all the same. Also, the feel on those keys is the same as the rest of the keyboard.
Same results with the grey label, none of the less-used keys felt any different than the rest of the 'board.
The feel difference may be because of the case quality or something like that because I also noticed a huge difference in the amount of resonance I got from the case.
The grey is a much quieter 'board than the blue. In general I do like the blue one more, but I haven't gotten a chance to like the grey one yet, and it is growing on me. Plus I like heavy switches, so we'll see...
Also, on another note, the text on the grey-label is a much lighter shade of grey than the blue-label(they're basically as black as you can get without double-shot)
Also, for all you crazy kids who don't care so much about these old BS folks, I have some interesting white-alps-ness on the way, soon as my adapter comes in(as long as it's not the XT version, then >.<)