I have made an interesting study. Amongst 342 of my favorite photographs (all from DPC), I analysed what kind of background was used. The results were as follows:
White : 81
Black : 81
Gray : 53
Context: 69
No Background : 37
Colored Background : 21
TOTAL : 342
It may be seen that white or black background was used in abot 24% cases each. (i.e. about half the images had either white or black background!)
In another 15% cases, the background was gray or off white.
Context served as background in about 20% cases only.
In about 11% cases, subject filled the frame, and there was no background as such.
Rest 6% of the cases had plain colours as background (with blue/skyblue being the most preferred colour).
These were the results of My favorite photographs. Personal preferences may vary.