As much as I try and wish to make this work in 10.5, it doesn't. Just another reason for me to upgrade sometime.

Copy works with other items in Spotlight as well. Copy a document and you can paste it else where in the filesystem, or paste its icon into a document, etc.

Wow... I'm not the first to go complaining about obvious hints because what is obvious to one may be obtuse to another. It is clearly intuitive and within the norms of OS X operation, but I had not discovered this previously (and had on occasion wanted to copy the Spotlight menu's calculator results.)

Interestingly, (and I'm on 10.6.4 here as well) selecting another Spotlight search item and using the copy shortcut copies the path to that item - assuming you don't have the text within the Spotlight search field itself selected!

I think when I'd tried this in the past I must have entered my calculation, closed the spotlight menu, gone back in and wanted to look at the total again, at which point the search text is highlighted, so hitting command-C gets me 100+4 instead of any generated Spotlight menu items.

Thanks - a useful, if intuitively obvious, hint!
g=

The calculator also 'knows' trig functions sin, cos, etc, exp (functional notation for e^x) and natural & common logarithms, factorials (even for non-integer arguments), and others. The shift operators ">>" ans "<<" are implemented. What's nice is constants like 'pi' and 'e' are available, too. (bc anyone?)