Res independence woes

How comes when I have RI on, it blurs out (slightly) some of my images when I build or view on the phone
(and yeah, I have checked all the width and hight are even numbers, and divisible by 4 (<<is that needed?)
Some graphics look fine, and others are a bit blurry.
Anyone got any tips?
I have just done a build without RI turned on, and it looks reallllly nice on my 3GS.
But runs a little choppier, which sucks.
Comments
That might be it!
QS
Also go through your blurry actors and open each instance and click revert to prototype you may have changed dimensions slightly when moving around.
(like I say, when I dont use RI it looks ace)
Just tried Jon's theory of making sure they are on even X and Y values...but still a bit off