Copying files into Dropbox folder from command line
Your script will be a lot easier to read if you expand the long statements to multiple lines:

@echo off
set dropbox=%userprofile%\dropbox
if exist %dropbox% (
    if not exist %dropbox%\%2 mkdir %dropbox%\%2
) else (
    echo Get Dropbox for PC before using this!
)
if exist %dropbox%\%2 copy %1 %dropbox%\%2
@echo on


Is that @echo on at the end necessary? Probably not, but I don't have a Windows with me to play around to verify.

The last if statement is pointless to execute if the first if statement was false. It would be better to move this inside the first if statement:

@echo off
set dropbox=%userprofile%\dropbox
if exist %dropbox% (
    if not exist %dropbox%\%2 mkdir %dropbox%\%2
    if exist %dropbox%\%2 copy %1 %dropbox%\%2
) else (
    echo Get Dropbox for PC before using this!
)


Possibly an even better way is to use the equivalent of an early return,
by leaving the main execution path when something is wrong.
You can do this using goto :eof.
After this the else statement can be flattened:

@echo off
set dropbox=%userprofile%\dropbox
if not exist %dropbox% (
    echo Get Dropbox for PC before using this!
    goto :eof
)
if not exist %dropbox%\%2 mkdir %dropbox%\%2
if exist %dropbox%\%2 copy %1 %dropbox%\%2


Rather than using the meaningless symbols %1 and %2 throughout the script,
it would be better to put these values to variables with descriptive names, for example:

@echo off
set source=%1
set target=%2
set dropbox=%userprofile%\dropbox
if exist %dropbox% (
    echo Get Dropbox for PC before using this!
    goto :eof
)
if not exist %dropbox%\%target% mkdir %dropbox%\%target%
if exist %dropbox%\%target% copy %source% %dropbox%\%target%