Here is a quick test of usability of the A12 28mm with mounted Ricoh wide/tele extension lenses. Of course, none combination matches the original image quality and corner sharpness of the 28mm lens. However, there are some surprises
The best combination seems to be the A12 28mm + GW2. It was a bit of surprise to me because from my previous test with GRDIII, the GW2 appeared to be slightly less sharp than DW6. With A12 28mm it looks very usable in case one needs something wider than 28mm? The DW6 makes the A12 28mm smaller and lighter, but at pixel level you can clearly see the corner degradation.
The second surprise to me was the GT1. Previous GRDIII test proved that the GT1 is unfortunately useless with GRDIII because of heavy corner unsharpness. And with A12 50mm it turned the very fine GR lens into a lensbaby kind of glass, good only for special occasions. However, with A12 28mm it appears to be way better than with GRDIII. True, there is still some unsharpness visible in corners. But it's not that bad and can be further improved by shooting in 4:3 mode.
The TC1, as I expected, is in my opinion a waste of time. It shows heavy corner vignetting even in 1:1 mode. True, the central sharpness is not bad, but I see no good reason to use this lens with A12 28mm?
Here you can see how the A12 28mm look with attached lenses. If viewed on 1440x900 or equivalent resolution on 15" LCD, you can get an impression of nearly 100% size of the camera with attached lens.

- GXR A12 28mm + GW2 (21mm)
- A1228_gw2.jpg (344.77 KiB) Viewed 20243 times

- GXR A12 28mm + DW6 (22mm)
- A1228_dw6.jpg (331.01 KiB) Viewed 20422 times

- GXR A12 28mm + GT1 (40mm)
- A1228_gt1.jpg (321.42 KiB) Viewed 20327 times

- GXR A12 28mm + TC1 (53mm)
- A1228_tc1.jpg (322.27 KiB) Viewed 20680 times
And here are the views (starting from the most wide):

- 21mm (GW2)
- A1228_21mm_sm.jpg (364.49 KiB) Viewed 20824 times
- EXIF-Data
- Image taken on: Sat Dec 04, 2010 1:15 pm
- Focus length: 18.3 mm
- Shutter speed: 1/380 Sec
- F-number: F/8
- ISO speed rating: 200
- Whitebalance: Manual
- Flash: Flash did not fire, compulsory flash mode
- Camera-model: GXR A12
- Exposure program: Aperture priority
- Exposure bias: 7/10 EV
- Metering mode: Pattern
Full sized photo can be seen
here

- 22mm (DW6)
- A1228_22mm_sm.jpg (357.06 KiB) Viewed 20796 times
- EXIF-Data
- Image taken on: Sat Dec 04, 2010 1:16 pm
- Focus length: 18.3 mm
- Shutter speed: 1/380 Sec
- F-number: F/8
- ISO speed rating: 200
- Whitebalance: Manual
- Flash: Flash did not fire, compulsory flash mode
- Camera-model: GXR A12
- Exposure program: Aperture priority
- Exposure bias: 7/10 EV
- Metering mode: Pattern
Full sized photo can be seen
here

- 28mm
- A1228_28mm_sm.jpg (407.27 KiB) Viewed 20644 times
- EXIF-Data
- Image taken on: Sat Dec 04, 2010 1:12 pm
- Focus length: 18.3 mm
- Shutter speed: 1/380 Sec
- F-number: F/8
- ISO speed rating: 200
- Whitebalance: Manual
- Flash: Flash did not fire, compulsory flash mode
- Camera-model: GXR A12
- Exposure program: Aperture priority
- Exposure bias: 7/10 EV
- Metering mode: Pattern
Full sized photo can be seen
here

- 40mm (GT1)
- A1228_40mm_sm.jpg (440.97 KiB) Viewed 20771 times
- EXIF-Data
- Image taken on: Sat Dec 04, 2010 1:19 pm
- Focus length: 18.3 mm
- Shutter speed: 1/270 Sec
- F-number: F/8
- ISO speed rating: 200
- Whitebalance: Manual
- Flash: Flash did not fire, compulsory flash mode
- Camera-model: GXR A12
- Exposure program: Aperture priority
- Exposure bias: 7/10 EV
- Metering mode: Pattern
Full sized photo can be seen
here

- 52mm (TC1)
- A1228_52mm_sm.jpg (489.6 KiB) Viewed 20741 times
- EXIF-Data
- Image taken on: Sat Dec 04, 2010 1:20 pm
- Focus length: 18.3 mm
- Shutter speed: 1/270 Sec
- F-number: F/8
- ISO speed rating: 200
- Whitebalance: Manual
- Flash: Flash did not fire, compulsory flash mode
- Camera-model: GXR A12
- Exposure program: Aperture priority
- Exposure bias: 7/10 EV
- Metering mode: Pattern
Full sized photo can be seen
here