If I may interject at this late stage; I use two tools;
SymmTime and
Downloader Pro. As was already pointed out its essential to have your cameras' clocks synchronized so I use SymmTime to connect to a
Stratum 2 NTP Time Server (I live near Chicago so Argonne National Labs is the closest official time server to me).
Once my computer's clock is set correctly I simply connect each camera to the computer via USB cable and run Downloader Pro. The "Camera Settings" dialog box in DLPro allows you to automatically synchronize your cameras' clocks with your computer (unfortunately this module only works for Canon cameras).
I then proceed with my shoot then download and automatically rename my files via an external reader and Downloader Pro. My preferred file renaming format is JAN_2''9'1'8_xxxxx (my initials; ISO 86'1 international date format, and a unique 5-digit number). But its worth noting that with DLPro you can use several "tokens" in your file renaming scheme that will identify your camera make, model, or even unique serial number from the EXIF data. So you can easily rename your files JAN_1Ds_2''9'1'8_xxxxx or JAN_1D MkIII_2''9'1'8_xxxxx. I previously named my files like this but I thought the names were too long and its also easy enough now in Lightroom to search for images shot with a particular camera so I shortened my naming scheme.
The last step in the process is to use BreezeBrowser Pro to cull my images, sort them by Time Taken, and Batch Rename to ensure no gaps remain in the file numbering. My reason for using BB Pro is that its one of the few programs I know that accurately reads subsecond timing; Lightroom seems to get confused sometimes when sorting photos shot in burst mode.
Then its off to Lightroom to generate and import DNG files while the RAW files are backed up to an external drive and DVD. I sometimes use 3 or 4 bodies in a shoot and this process ensures that my files are always correctly arranged by time sequence.