One of the things that I loved about Toastmasters is that they designated someone to be the "um grammarian." Their job was to count how many times you used filler words or unnecessary pauses. Very frustrating at first, but damn it really made me a better speaker. Because of that brief experience it is kinda hard to listen to Obama talk sometimes, sometimes he has the MOST unnecessary ummm and ahhhs.
So native english speakers avoid "ummm", but english learners should actually make it a habit. Likewise, when learning a foreign language, native english speakers should make a habit of adopting that language's filler words. Especially because you will be using it so often while trying to remember vocabularly.
For example, if you are learning spanish, use drawn out "pues" or "este..." to interject your broken spanish and you will insantly sound more fluent. Not "ummmm" which sticks out like a sore thumb to native spanish speakers. Chinese speakers learning english will sound better using "ummm" instead of "aaaahhhh". And german speakers instead of "zee...". I'm not sure how to phoneticize the Indian filler sound (anyone? :)
Point is, as a foreign learner, the quicker you can adopt the native filler the better you will sound, because you will be using it quite often.
http://www.nytimes.com/2012/10/03/opinion/jerry-seinfeld-rea...