Just a brief of my experience for Russian visa. Actually I flew to Washington, D.C. Office and personally applied for a 3 year multiple visa. The visa inspector was very nice and she told me I had three mistakes in the form and also Marriot hotel in Moscow who had issued me free invitation letters had put my wife's passport number incorrectly . But she was very helpful she went back and corrected all the mistakes in the forms and let me call Marriot hotel in Moscow request them to send another invitation with correct passport number and when I received it after 15 minutes she let me forward to her email so she can print it out.guess what? This time they had spelled my wife's name incorrectly and I went thru the same process of calling them and sorting it out. All this took about 2 hours and she patiently worked with me to correct every situation so my visa would not get rejected. Though I paid $25 extra for correcting the application it was well worth it.
If you go in person things do get faster and also they won't accept the application till everything is ok. My advice go personally if you do not have much time.