Getting rid of PPC code won't increase performance at all. It will ONLY save you disk space.
Back when I used Xslimmer (before I got enough disk space not to worry about it) the only problems it caused were with Adobe CS3.
If you want to increase performance, look for unnecessary third-party add-ons to your system and get rid of them; make sure you're not using any PPC apps (look in the Activity Monitor with the "Kind" field enabled); make sure you're quitting apps when you don't use them; restart once in a while; and most importantly, buy as much RAM as your Mac can hold.
I didn't say for sure that it's speeds it up, I only said it shoud not break down the performance.
And just thinking logical, the OS has to determine each start which code it will run. Sure that only takes a nanosecond. Because you don't realize that nanosecond, yeah it's not supposed to be any snappier.
Buying more ram isn't needed. He won't even need the 2 gigs which he already might have. Just look in Activity Monitor how much really is used. I bet he doesn't do any video encoding/converting and stuff.
Ok, if you want to spend the money on more RAM, go for it (it's pretty cheap), but beside the little improvement in appliqation startup it won't help you in your daily working.
@aznelementmaste: does dis greying-out only happen at the very first oppening of an app (like after restart) or everytime you click on it in the dock?
I have sometimes a little lag with iTunes, but sometimes it just opens stright away. But that's because my iTunes library is huge (I have found out that above 80 gigs or so it gets a few slower starting/quitting), so I won't complain about my little lagging which happens from time to time.
I am rarely using the other Apple apps, (I use Firefox+Thunderbird mainly. Rarely iPhoto and the Calender.)
And until everything is still fricking fast I just can't complain about it.
I don't think I can help you any further without knowing more (Do you also have a big iTunes/iPhoto library. Do you regularly restart or shutting down in the evening. Is your HD getting full?) there are just too many factors which could influence the performance.