Exporting multiple different sizes from Lightroom

[Update 17/2/2012: Modified the script slightly to fix a path capitalisation bug]
[Update 22/3/2013: Re-recorded the video to explain the process better]
I've been shooting a lot of model sessions lately and one of the things I always need to do after these sessions is put the processed pictures into my dropbox where the model can see them. These pictures are for a variety of different uses including Facebook, 500px, Google+, various modelling sites and, of course, print publication. 
These sites often have different size limits and requirements so I usually need to export versions with and without watermarks and at various different pixel dimensions. So it's always been a pain in Lightroom that I can only export images at one size. Here's what I export by default: 

full-size clean
full-size watermarked
2000px watermarked
1000px watermarked

That's 4 separate exports and of course I have a preset for each. It's not a *lot* of work but all those clicks bug me so I set about finding a way to export multiple different sized versions in one step. I tried a number of different approaches but the one I settled on was to write an application. Steady-on, it's not as scary as it sounds. My plan was to set up an export preset to save a full sized watermarked version then my application, called automatically from Lightroom, would take that full sized version as input and create 2 more smaller versions and save them in the same folder. The problem now, was writing the application. 
I'm on a Mac so I started looking at Automator and when that proved too limited I looked at Applescript and when that proved too hard to debug I did what any reasonable, right thinking person would do and started whining on Twitter. I have a background in programming so surely I could accomplish this apparently simple task but no, I'd wasted a whole day on this so finally I asked for help. And to my great joy a couple of people did try. I posted my broken Applescript on pastebin in a huff and the next morning John Day (@johneday on twitter) had completely rewritten and simplified it for me. Thank you so much John - you're a superstar. Here's the script he wrote for me:
on open of myFiles
set newSizes to {1000, 2000}

repeat with aFile in myFiles
set filePath to aFile's POSIX path
set bPath to (do shell script "dirname " & quoted form of filePath)
tell application "System Events" to set fileName to aFile's name
repeat with newSize in newSizes
do shell script "sips " & quoted form of aFile's POSIX path & " -Z " & newSize & " --out " & quoted form of (bPath & "/" & rename(fileName, newSize) as text)
end repeat
end repeat
end open

on rename(fName, fSize)
do shell script "sed 's/fullsize/" & fSize & "/'