kathye,
we use the trimming from both our sour orange tree and lime trees for smoking (the lime leaves i use when thai cooking) just be sure they are dry before you put them in a cs. kumquat would be neat to try!!!! i find the citrus wood works best on chickens or ribs. leaves a nice color a little lighter than the mahogany that pecan gives me but pretty close and the flavor is good.
someone once gave me advice that if the tree bears nuts or fruit that you would eat it was ok to try and so far that advice has been good. just be careful with black walnut though it can bitter up real fast like miskeet
jack
ps. and with that i am off to watch the bbq comp on food network from mandaly bay.