Hi parkes,
I guess if you use the 45mm a lot, then chuck on the 90, you go WOAH, the frame seems ALOT smaller, in both length and height.
The lines of the 45 arent full, meaning theyre broken up somewhat, and sometimes i find myself really trying to judge if i am cutting off the top of a tree for example. Mines xpan 2 so i also have the exposure box in the frame as well.
The 90 however, is more of a complete box, so in that respect composition i guess is a little easier, although you dont have as great field of view as you do with the 45.
I like it, its a great lense just like the 45, but for me it has limitations on what i can use it for, therefore it doesnt see as much action as the 45. I have done some good shots using it with closeups of things like pattens on tree trunks and the patters on sand dunes etc...
As far as the real landscapes go... it stays in my camera bag.
If you can get it for a good price, then id go for it!..
Hope this helps