I got sick of copy/pasting to "assemble" a link from my smugmug gallery, so I spent a bit of time over the past day and managed to cobble together a Grease Monkey script that will put together the UBB code for a particular picture when you click on the Share | Get a link option for any image. It will add a text box at the top of the page. The default code will have the link to the LightBox of the image and will show the medium sized image. Those options can be edited in the script towards the top; there is some documentation in the comments for how to do it.
The code looks like this:
[URL="http://gallery.millerworks.net/gallery/7770679_V8fYm/1/#502752747_KJN8q-A-LB"][IMG]http://gallery.millerworks.net/photos/502752747_KJN8q-M.jpg[/IMG][/URL]
and results in this being displayed:
You can get a copy of the GreaseMonkey script here:
http://old.wanderingaramean.com/smugmug-UBB.user.js
Once you've installed the script you'll need to manage the included sites bit through the GreaseMonkey interface to reflect your personal smugmug account.
ETA: This was all well and good, and the original script is still online, but it turns out that it no longer works and it is wholly unnecessary. SmugMug has updated their systems to now essentially provide the results that my script does and they do it natively. Just chose the BBCode-Medium line on the Embeddable Links page when you go to share an image.