Most traffic sources require you to entire a blacklist in CSV format, so a list of placements like this 1234,1235,1236 etc
When handling a lot of data, the quickest way for me to do this is usually to export a
At this point they are in a list format, so now copied to clipboard, I paste to the first column in mergewords.com, and in the second column I add a comma ",". Next, click the extra options and select the seperator "nothing" and then click the "Merge" button.
Copy the resulting list and paste here - Click "remove all line breaks" and you should have your resulting blacklist ready to be entered on your traffic source.
There are probably other ways, but this takes me less than a minute to do!
Note: You can save data from spreadsheets as .csv but depending on the software you use, the output can vary. OpenOffice for example will save as .csv but when opened in notepad it's still in list format.
Or.
You could use this http://delim.co 
Nice, glad I shared the post.. thanks for the link!