On looking at Works again, I see that text characters aligned right (by reformatting) are distinguishable from numeric values (aligned right by default) by the absence of a space to the right of the text characters. So text can normally be detected at a glance even when reformatted right.
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To summarize:
If all the cells contain numerics the spreadsheet looks like this with a space to the right of the numbers and the sum is correct:
If the A3 cell contains text with default formatting it looks like this and the sum is incorrect:
If the text in A3 is then manually aligned right it looks look like this with no space the right and the sum is still incorrect:
Now of course if you really want to shoot yourself (or somebody else) in the foot you can add a space to the right of the text so that everything lines up nicely. Everthing then looks right but the sum is wrong:
As I said above, this is in Works. Perhaps someone else can check what happens in Excel. Have fun.
