There's an awesome plugin for uploading directly from LR, get it
here.
If you wish to use MacDaddy, proceed with the below :)
First, you'll need to get SmugMug's MacUploader. In your gallery, click "add photos" and then follow the link for MacDaddy.
Help.
Click on the first image in this gallery to enlarge it. Click "next" to advance to the next step.
These first few steps only need to be done one time, to get things set up.
1) Open your Applications folder in Finder. Right click on SmugMug MacUploder - then click "Make Alias."
This will put "SmugMug MacUploader Alias" right beneath your current SmugMug MacUploader.
2) Move this finder window off to the side - we'll come back to it shortly.
3) From within Lightroom, choose "Export" from the file menu or by right clicking on a photo or thumb, then choose "export" again from the fly-out menu.
4) From the export window, look for the "After Export..." pull-down menu. Choose "Go to Export Actions Folder Now." That will open a new finder window.
5) Open the Export Actions folder.
6) Go to your Applications folder, and drag the "SmugMug MacUploader Alias" into the open Export Actions folder.
7) It should look like this now. You're all done with the set-up!
OPTIONAL: You can rename this alias - anything you want, really - just click on the file name and change it.
Now that you've set things up, here's how to easily upload from lightroom to SmugMug:
In Lightroom, when you choose File>Export, or right click on a thumb, or batch of thumbs, and choose "Export > Export" you'll see SmugMug in the "After Export" list.
Just click the "Export" button.
Your photos are ready to go!
The last step is to choose the destination gallery or make a new gallery and click "upload."