Transcription Methods/Times
Speech Detection with Adobe Premiere

You haven't mentioned what NLE you use to edit, however here is a method you can use to transcribe if you are using Adobe CS4 or later. 

This method uses speech detection to automatically transcribe videos - a feature brought in with CS4. It then adds the the text into the metadata of the file. 


  Analyze speech to create text metadata
  
  
  Select a file or clip.
  At the bottom of the Metadata panel, click Analyze Speech, or Analyze (Adobe Premiere Pro).
  Set the Language and Quality options, and select Identify Speakers if you want to create separate speech metadata for each person. 
  Note: Speech Search can use any of several language-specific and dialect-specific libraries, such as libraries for Spanish and UK
  English.
  Click OK.
  The spoken words appear in the Speech Analysis section.
  
  
  To retain the speech metadata, save the project.


Obviously this depends on the quality of the audio. Good clean audio will provide the best results. Its also worth noting that Premiere uses Soundbooth to process the detection, so if your audio wasn't up to scratch you could clean it up in Soundbooth, and then perform the analysis there. 



VLC Scripting

I came across this article explaining how to take the current timecode from a video and add it to a text document for transcribing. The title of the article states its a method for Linux. However I'm sure it would be easy enough to take the method and apply it to Windows or OSX.



Manual

In regards to your current method, it depends on how many times you fall behind. When I have transcribed video I have done it at full speed but I haven't bothered to fix errors while I'm typing. Usually I'll go back and fix it up later - and being that they are just for editing purposes they don't need to be totally correct. 

Manual live tagging with Adobe Prelude

You might also want to have a look at Adobe Prelude CS6. It's an ingesting and meta logging program. One of its features is that it lets you add markers (and name them) in realtime as you are watching the video.