Wikipedia has this to say about and/or:

And/or is a phrase used to indicate that one or more of the stated cases may occur. For example, the sentence "Jim will eat cake, pie, and/or brownies" indicates that although Jim may eat any of the three listed desserts, the choices are not necessarily exclusive; Jim may eat one, two, or all three of the choices. 

As the phrase has grown in usage in recent years, from business jargon to legal writing and popular culture, it has likewise come under criticism. Some grammarians have pointed out that the phrase is redundant, since the word "or" logically and grammatically encompasses the same meaning. That is, the sentence "Jim will eat cake, pie, or brownies" still permits Jim to eat one, two, or all three of the choices.

Others argue^[who?] that in a very legalistic society, the word "or" is no longer sufficiently clear, because it may indicate choices that are mutually exclusive (see exclusive disjunction). The word "and" by itself is of no help here, as it requires that all of the conditions are met; in other words, that Jim will eat all three of the choices. Thus, they argue, "and/or" serves the function of clearly indicating that every case is available and that they may be combined.

In comp sci, a use of or called the logical OR negates any necessity of and/or, since it is the same, I believe, @ least to some extent.

I have the following to say about an/or (which I had to alter in the link to make the link valid, since it did not "like" my slash):  See my entry on the logical OR.

and/or is 'nother 1 them thangs you'll find I use allot.  I was thinking of writing that I wondered what such indicated about me, but Wikipedia has offered an answer about such.  Apparently it means I'm legalistic.  A claim I would feel no obligation to counter, nor any shame for not countering.  MabFrontPagey I'll create a link to exclusive disjunction.