Having just typed all that - I see things have progressed a bit....
Molgrips - you're point about the family shot to me underlines the point i'm trying (badly) to make.
The zoom lens in convenient - in your case it made it easier for you to get the shot you wanted. Nothing at all wrong in that, nothing at all. On 'family' days i'll most likely have a zoom on there as well...
However, had i been out with just, lets say a 50mm prime, on there, and the shout goes up for a family shot I either
a. make the space I need - as you say, not always convenient.
b. think 'f'it - can't be bothered to move / wrangle the family and not get a shot at all'
c. quickly (and it does not take long) reshuffle the family to fill the frame in the space you've got.
Finally (on lens choice) I use zooms 99.9 % of my working life as they are, for want of a better word, convenient - i chase around enough at a wedding or lifestyle portrait shoot, without adding more running back and too into the equation Making a serious point of this wee statement - perspective - I tend to work mostly at the 200mm end of my zoom @ F4 = isolating figures from the landscape around them, whilst not being in their face with the camera.
That said, the most fun I've had with my camera this last year was a shoot out and about with fellow photogs - I chose to just use my D700 and 50mm 1.8 lens.
Edit - Right - that's it - i'm way behind with edits on two shoots that are promised to be online for tonight (and I'm an hour late going home to walk the dog!) so, whilst i'd like to add a couple more thoughts = molgrips has raised the most important thought - have fun and enjoy what you're doing - if (for example) 'round face' portraits make you smile, have fun with your family whilst improving your skill levels with that particular technique
Ok, one final thought - aim to get the shot right in camera - saves a lot of time 'saving' shots in your editing software. Getting to know your kit, and how it works / how it does not work (even top end pro stuff is far from perfect). It takes a little time to master but, once you have, the time is more than paid back - I shoot almost 100% on manual now. I can take a shot, tweak the exposure and take another one typically a lot, lot quicker than a poorly exposed one can be corrected in the editing... and, it is still, to me, a great feeling to see a correctly exposed / framed image pop up on screen.
Right, dog walking beckons....