I have this change on my U-12 on RKL, lowering the 6th string to G. I also raise the 9th string from Bb to D on this lever and lowering the 2nd string to D as well.
My setup can be seen here.

I find it extremly useful. Here are some examples:

Eks 1: - The most obvious one is that you'll get a minor 7 chord (lowering the third.)

E minor chord.

1-----
2--0L---
3-------
4--0----
5--0----
6--0L---
7-------
8--0----
9--0RRR-

Eks 2: - If you bring in the 7th(lowered 2. string) and major third(3. string) this gives you a really dissonant #9 chord.

E#9 chord

1-------
2--0L---
3--0---- (major 3)
4-------
5--0----
6--0L--- (minor 3)
7-------
8--0---- (Root)
9--0RRR- (7th)

Eks 3: - Holding down both A & B pedals, releasing the B and then bringing in this lever gives you a nice 7. chord with a chromatic walk down to the 7th.

From A to A7

1-----
2-----
3-----
4--0~~~~~~~~~~~~
5--0A~~~~~~~~~~~
6--0B~~~0~~~0L~~
7-----
8--0~~~~~~~~~~~~

Eks 4: - Combining the lowering of string 6 and raise string 4 also gives you a nice G7 chord with the fifth (D note) on string 9.

1-------
2-------
3-------
4--0R---
5--0----
6--0L---
7-------
8-------
9--0RRR-

Eks 5: - Sliding from one 7 chord to another.
From one G7 chord to another G7.

1--------------
2--------------
3--------------
4--12R~~~~10~~~
5--12~~~~~10A~~
6--12L~~~~10L~~
7--------------
8--------------

A standard jazzy sequence could be Dm7 - Db7 - Cm7 - B7 - Bbmaj7
With this change I get that easy on U-12:
Eks 6:

    Dm7    Db7  Cm7   B7
5-----------------------------
6---10L----9----8L----7----6--
7-----------------------------
8---10-----9LL--8-----7LL--6L-
9---10RRR--9----8RRR--7----6--
10----------------------------
11--10-----9----8-----7----6-- (root)
12----------------------------

This change is also great for playing chromatical scale patterns. By the way I play with four finger picks.

Comments anyone?