1) People tend to expect things to be left-aligned unless they specify
otherwise or there is some special reason to make that element more
noticeable (such as a level one heading)
2) I personally think it makes documents hard to read when two tables in
succession do not align their left sides, so your eyes have to constantly
adjust for this when comparing or correlating information in the two
tables
I can see how figures might be better off center aligned (though I'd vote for
justify myself) but I really think tables should be left aligned by default.
Michael Johnson
Relay Technology, Inc.