One problem I face constantly is that file formats do not necessarily transfer from Windows to Linux. I use OpenOffice, which very few people at Northwestern uses, so often I have to safe it as a Word file or a PDF document before sending it out. The conversion problems aside, sometimes I may be dropping by the computer lab to print something I had planned on printing later. I ssh into my laptop, and find that I haven't converted the document yet. Since the university computers do not have OpenOffice either, I can't open the file.
Zamzar is an online file conversion service, with a wide range of file formats to convert to and from. Not only does it do documents, but it can also handle images, videos, and compressed files. It should provide 99% of every day needs, especially if people are desperate. I just realized it doesn't support StuffIt files though, which is a shame since I still haven't found a way to open those on non-Mac OSes.
The last time I needed the service, I had to convert an OpenOffice document to PDF. If it was just text I would probably have opened it in Notepad and see if there's anything I can do (in old Word files you can see the text, without formatting of course). However, it was a stats homework, and I had a number of OO Math equations embedded in it. The first thing I tried was attaching it to an email and sending it to myself, knowing Google could open it in Google Docs and save as PDF. It worked alright, except the equations were crooked.
So I used Zamzar. My only complaint against them is that the service is not instantaneous. I had to wait 10 or so minutes before I got an email with the download link. That file, however, was perfect. If I had saved it as PDF directly from OpenOffice it would have looked exactly the same. No doubt they somehow hijacked that portion of OpenOffice for this purpose. I printed the document and was on my way.
In summary, Zamzar is great for converting all kinds of files, especially if you can't do it yourself. The only down side is it's a tad slow, but that's far outweighed by the pros.