You asked for it, you got it--these are the most recent Sigma notices FROM SIGMA ITSELF, with URL's. Admission from Sigma itself that its products suffer from incompatibility issues with Canon and Nikon products. Please note--there are dozens more user-generated complaints and issues. The following are OFFICIAL, Sigma admissions of problems. Choke on it.
http://www.sigma-photo.co.jp/english/news/info_080527.ht
Official service notice FROM SIGMA, to Canon users, notifying them that their lenses 120-300 OS and 150-500mm OS: "When the Canon 40D digital SLR is in AI Servo AF mode, and the APO 120-400mm F4.5-5.6 DG OS HSM for Canon or APO 150-500mm F5-6.3 DG OS HSM for Canon lenses are attached to the camera with the OS function switched ON, the number of continuous frames per second will decrease.

To overcome this, we will start supplying a free-upgrade service to our customers from today.

We deeply apologize for any inconvenience this may have caused to our customers."
Sigma - News
0/31/2008
Notice to customers using Sigmas EO-ETTL II type flashguns
Sigmas EF-530 DG SUPER EO-ETTL II, EF-530 DG ST EO-ETTL II, EM-140 DG EO-ETTL II, EF-500 DG SUPER EO-ETTL II and EF-500 DG ST EO-ETTL II do not operate roperly with Canon EOS 50D D-SLR camera. To overcome this, we will start supplying a free-upgrade service to our customers today.
Please notice that this problem occurs with the EOS 50D D-SLR camera only.

We deeply apologize for any inconvenience this may have caused to our customers.

Upgrade will be required to overcome the following problems:
1. The Autozoom function does not work properly.
2. Exposure is not correct.
Notice to end-users using Sigma's HSM equipped lens with Nikon D200 camera
Sigma has issued a service notice for the use of their HSM lenses on the new Nikon D200 digital SLR. HSM or HyperSonic Motor lenses use a motor driven by ultrasonic waves to provide a quiet, high-speed autofocus (AF). Due to a firmware bug in these lenses, this function does not operate when the AF operation button on the back of the body of Nikon D200 digital SLR is used. In case the shutter button is used for AF operation, the camera and lens combination works without any problem. Sigma is committed to correct this situation and will start updating firmware of these lenses free of charge today.
From Sigma itself, "To our valued customers,
AF function of our HSM equipped lenses do not operate when "AF operation button" on the back of the body of Nikon "D200" digital SLR camera (recently introduced to the market by Nikon) is used. This problem is caused due to a firmware "bug" of our HSM equipped lenses.
We deeply regret any inconvenience this may cause our customers who own D200 camera and we are committed to making this situation right. In this respect, we will start updating firmware of these lenses free of charge today.
Please also note that if "shutter button" is used for AF operation of HSM equipped lenses, camera and lens combination works without any problem.
This problem occurs with *HSM equipped lenses only. Non-HSM models of Sigma lenses function properly with D200 camera.
Click here for a list of the US Sigma Distributors and Service Centers
Click here for a list of WorldWide Sigma Distributors and Service Centers
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Notice to Nikon D3 owners using Sigma’s Nikon fitting lenses - SIGMA CORPORATION
Notice to Nikon D3 owners using Sigmas Nikon fitting lenses
2008.1.21
A limited number of Sigma lenses when used with the new Nikon D3 digital SLR camera will not support the "Auto DX crop" function. To overcome this we will be supplying a free upgrade to our customers. We deeply apologize for any inconvenience this may have caused to our customers.
Sigma Corporation 2008/1/21
List of lenses requiring update for D3 camera
DC lenses (Exclusive for digital SLR cameras with APS-C image sensor)
30mm F1.4 EX DC HSM
Serial Numbers lower than 2054001
10-20mm F4-5.6 EX DC HSM
Serial Numbers lower than 2160001
DG lenses(Lenses for 35mm format SLR cameras)
APO 300mm F2.8 EX DG HSM
Serial Numbers lower than 3013701
APO 120-300mm F2.8 EX DG HSM
Serial Numbers lower than 4022401
Upgrade will be required for the following problems
1. When the Nikon D3 is in Auto DX crop function and the 30mm F1.4 EX DC HSM or 10-20mm F4-5.6 EX DC HSM lens is attached, the image area format will not change to DX format automatically.
2. When the Nikon D3 is in Auto DX crop function and the APO 300mm F2.8 EX DG HSM or APO 120-300mm F2.8 EX DG HSM lens is attached, the image area format will be changed to DX format, even if the image area format is set to FX format or 5:4.
For further information, please contact your nearest authorized Sigma Service Station.