It is a fabulous lens on full-frame, but for me it would also be the perfect lens range for your intended use on the D90, being a 36 to 105mm equivalent.
The usual fast standard zoom for a crop sensor is the 17-55 f2.8, but I found it a bit short at the long end for portraiture.
...... and then, when you decide you want a full-frame, the lens still works!
For the portraiture use that you have specified I would say that going wide is a bad thing due to perspective distortion. Consequently, a 24-70 on a cropped sensor gives you a better working range.
badboy1984 said:Cracking lens but I definite don't want to walk around in the street with that lens when going to trip/travel lol
I was thinking of this lens for my D7000, first main use would be on holiday. Why wouldn't you want to you it for that?