Now that the Messages app is available as a beta for OS X Lion and OS X Mountain Lion, there's a way that you can quickly send files from any Mac to an iPhone. Lifehacker tested the capability, and sure enough it works splendidly for zapping files to iPhones in the field.
Here's how to do it: open Messages on your Mac (you did download the beta, didn't you?), and address a message to an iMessages account on an iPhone. Instead of typing into the message field, just drag any file from your Mac and drop it onto the message field. Press the return key on your keyboard to send the file, and within a few seconds you'll usually get notification that it has been delivered.
On the iPhone, just open Messages and you'll see the file or files that you sent. Images usually come across as a small thumbnail -- tap on the thumbnail to view the image and save it to your photo library. Documents such as PDFs or Word docs can also be viewed within the limitations of the iPhone screen with a tap -- tapping on the Share button that appears gives you the option of printing the document or opening it in any compatible app.
This method worked well for a number of files of varying size and format. For example, everything from a 149 KB PDF to a 101.4 MB MOV were quickly dispatched to my iPhone with a drag and drop. I tried to throw a 194 MB MOV file to the iPhone, but was informed that the file was too large. The limit is somewhere between 101.4 MB and 194 MB -- I leave determining the exact maximum size as an exercise to the reader.