I have recently bought a D-10, having been a D-30 user since they came out. I also have a EOS-5 and IX-APS.
I originally bought the cheaper Sigma lenses with the EOS5;
28-105 f4/5.6
100-300 f4.5/6.7
I then added;
Sigma 170-500 f5/6.3
Sigma 28-70 f2.8EX
Sigma 70-200 f2.8EX
Sigma 28-300 f3.5/6.3
Sigma 14 f.28
Canon 50 f1.4
Cosina 19-35 f3.5/4.5
I found all the lenses worked acceptably with the D30.
Since the D10 arrived I have had some issues that have made me re-evaluate things a bit.
I had to send 2 lenses back to Sigma (170/500 & 28/300) for modification to cure the ERR99 problem.
Full praise to sigma service. They carried out the work FOC and extremely quickly.
Since the 28-300 has come back and I have tried to use it, I find that it still gives regular ERR99's. It also now has trouble with AF in lower light conditions, where it seems to hunt and then settle significantly out of focus. It also seems to sometimes stay stopped down after the shot is taken, leaving a darker viewfinder and wrong exposure for the next shot.
To be fair, I havn't had a chance to report this back to Sigma yet for investigation & rectification. I should stress that the lens seems to perform OK on the EOS-5.
By contrast, at the same time I sent back to Canon my 50 f1.4. This had literally 'fallen apart' with the rear lens dropping out and the whole assembly rattling. How this happened I do not know as this lens has had very little use and always travels in the camera bag with many other lenses. Canon charged me over £230 and took about a month.
When I originally bought this Canon lens, it stopped working (af failed), and Jessops replaced it as it was only a couple of days old.
Reliability and quality of service Sigma - 1, Canon - nil.
I have used the lenses for a couple of months on the D10 now and have always thought the results of the sigma EX's were soft and not accurately focused. This seems much more noticable on the D10 than on the D30.
Motor-racing shots taken with the Sigma 70-210 f2.8 seemed particularly soft, and the D-10 had real problems in AI servo mode keeping up.
I have just bought a Canon 100-400 f4.5/5.6 L U IS. I have to say that speed of focusing has improved considerably. Pictures now seem to have more contrast and focus seems considerably better. I have to say that I'm VERY impressed with this lens.
I have decided that I am going to get the Canon 16-35 f2.8 L U next. If this works as well as anticipated, a Canon 70-200 f2.8 L U IS will be added shortly afterwards.
The point I am making here is that my progression of equipment has shown that as the camera resolution has increased, issues with the Sigma lenses, not apparant with the D30, have appeared.
While I found the combination of my Sigma lenses and D30 camera to be very good, the D10 has raised the game to the point where I feel that I need to use Canon L lenses to get the quality that I expect.
I could, of course have been unlucky with some lenses, but you can see that I have a wide range of Sigma lenses, and remain a fan.
I will probably continue to use the D30/Sigma combination as a backup system, but only buy Canon L for the D10 (and maybe 1-Ds one day).
I am doing something wrong, I am seeking enlightenment !
Sorry this has been a long first post, but thought my experiences may be of interest to the forum.