I'm not quite sure how to point this out without exuding self-entitlement and so on ... so I'll just put it out there.
As of tonight, I have about 25 new documents from this evening entitled 'homework' or 'homework_3' or 'hw' or some variant. I have little folders with your names that contain these documents in order to keep them straight, and a hierarchy of folders to distinguish different homework sets. There is a complicated system in place. Worst case, I can always go back to the original email if I am not 100% sure. So far, and for the last few semesters, it works. I also try to acknowledge receipt as quickly as possible.
However, it would save a lot of time for me if the files you sent me contained your last name in some way. When I get a file named "homework.pdf" I can't just hit "save attachment" and select the homework directory, or chaos ensues. If isn't a huge inconvenience, naming the files cleverly before you send them to me helps a lot. Again, I'm not suggesting my time is more valuable than yours, but there are roughly 25 of you submitting homework electronically and one of me. Another good thing is to make sure your name is written on the first sheet before you scan, that is another helpful failsafe.
I don't mean to inconvenience you - I will still accept files labeled "homework.pdf", "physics.pdf", and "SCN9211523.pdf" if you can't do otherwise, and will meticulously keep track of who sent which files when, but you can help make this process more efficient.
Don't get me wrong, I do really love the electronic homework. Giving you the ability to attach Excel or Matlab files to solve numeric problems is much more efficient for both of us, if that is your preferred mode of solution. It also eases the communication barrier and time pressure, I think. There is something really cool about getting homework submitted via iPhone, for instance, or receiving a nicely-formatted spreadsheet, I have to admit. My main point is that more options can breed more obfuscation if you're not careful. While I can deal with a myriad of file formats and odd file names, the next person might not bother ... e.g., applications for jobs or internships.
Finally, there is nothing wrong with hard copies shoved under my door. Don't feel pressured to submit electronically or make complex spreadsheets if you prefer pencil and paper. I'm just leaving that as an option for you, if that's how you roll.