>. Back in film >days before zoom lenses really became viable, I had 28, 50 and >135. In DX terms, that's 18, 35 and 90 - with nothing in >between!
In a way I agree with Brian here.
When I look at the lens selection I had for my Pentax SPII, I had a 28, 50 and 200 with a 2x converter. Ahhh!! The good old days.
Early on with my first DSLR my main lenses were the 17-55 and the 70-300 VR. For the most part I did not miss the range in the gap. But recently I brought my camera to our Obedience Clubs competition which was indoors. I quickly learned that that gap would have been useful in the confined environment I now found myself in.
So as suggested, take a look at your images and see how many of them are shot in that range. While it won't predict any future need, it will tell you if you would immediately miss it.