Both DS's have fairly small rooms and haven't expressed an interest in their own trees, tabletop or otherwise. As teens, their idea of decorating is to squish down any big blanket lumps on their beds and pick their pillows off the floor.
DD has a pink tabletop tree. She loves to make decorations for it, but she really wants a bigger tree in her room. She has room for it, so maybe she'll get one some time.
For '08, we're planning to put lights up in their windows, and I'd like to get them flannel sheets. I LOVE the idea of putting a wreath on each kid's door that reflects them somehow! DS15 would be decorated with guitar picks and guitars (or car keys and road maps, as he turns 16 just after Christmas next year!), DS12 would have drums or skateboards, and DD's currently would have pictures of Hannah Montana! We'll have to wait and see what her interests would be this coming Christmas.