Actually, the NT3 IS a good mic for filming. The pick up pattern for it is hypercardioid which is not as directional as an NTG 3 or MKH 416. Shotgun mics don't always sound good indoors.
The mics also sound quite good in terms of price to performance ratio
http://dvestore.com/theatre/mics_guide.html
This microphone shootout done by dvestore demonstrates the differences in performance. The NT3 and the MKH 416 (in my opinion) sound the best out of what was tested.
I know these microphones were awfully close to the VO person so here is a youtube video of some people using these mics for their cameras.
http://www.youtube.com/watch?v=lEa7uGyXl-8
This one was put on a boom about a foot and a half above the subject. Close but hardly a few inches in front of the mouth.
http://www.youtube.com/watch?v=T813-ugJfR8
Here is another example of the NT3 replacing someone's internal mic on a DVX100A
http://www.youtube.com/watch?v=ETX_nBG9zvU
This is another promo video from dvestore explaining why hypercadioid in some ways is better than shotgun for indoor use. (I'd like to state that I have no association with them, they just have the videos that are easiest to prove my point).
If you look you'll find other videos like these all over the internet.
For professional broadcast or film audio it's not unusual for an audio guy to carry
Lav mics - for wide shots that would expose a boom mic (if you don't just ADR it)
Hypercardioid mics - for indoor environments
short and long shotgun mics - for outdoor or indoor
The truth is a lot of schools (even some film schools) beat the idea of a boomed shotgun mic so thoroughly into students heads that they assume any other way is wrong.
Granted you still need a shotgun mic for the outdoors but for indoors I wouldn't hesitate for a second to pick a good hypercardioid microphone over a shotgun (be careful however when booming, hyper mics are usually heavier than shotguns).