It may possibly just an issue with ubuntu's version of compiz, but on my machines I noticed there seems to be a delay when it comes to how fast new windows open, and the minimize animations sometimes lag a bit. I think its something to do with the animations plugin. The "minimize effect" plugin doesn't seem to be in ubuntu anymore but using that instead of animations always made compiz way smoother to me, opening windows especially seemed way faster and the minimize effect rarely lagged. For me the best version of compiz was 0.8.4. I used it recently when I tried linux mint debian and it seemed so much more responsive than recent versions of compiz. For me mutter just seems more reliable than compiz ever did.
On my ati card specifically I have this awful issue with newer versions of compiz where if I enable smooth scrolling in any program its horribly laggy, I didn't have this issue in the older version of compiz in LMDE though, and didn't have it with mutter.
I may have been exaggerating when it comes to how much "lag" there is, theres really not that much, its perfectly usable, but I have high expectations of how smooth the composited desktop should be. I've never had these types of problems with aero or windows for example. I've never seen an animation lag or anything with that, and compiz never really reached that standard for me.
I sure understand you, I also find that compiz 0.9 is somewhat laggy.
I also now use compiz 0.8 because of that.
Although over all the reason why I use 0.8 is that 0.9 totally fucks up the notification bar support and I need it a lot in KDE.
(I use gnote, nm-applet, and couple more apps that need that tray)
KDEs NM applet is buggy (because NM is gnome-centric and the devs don't care about updating KDE support)
in my point of view unity and gnome can die... i don't need it.
I'm also a KDE user, and I love KDE 4.4 on my desktop. Despite many people says Kubuntu is a poor implementation of KDE, I prefer it over any other distro excepting a pure Debian.
But I don't hate GNOME. My laptop runs Ubuntu 10.10 with GNOME 2.x, because is much faster, memory efficient, its NetworkManager applet works better that the KDE/Plasma version, and does not do stupid things like running the Nepomuk - Strigi megabloat by default.
I dislike Pulseaudio; it makes KDE very unresponsive. Even if it's possible to run all KDE 4 apps over ALSA, they'll be muted the first time any Gtk-based app attempts to output sound (Firefox comes to mind).
JACK is an excellent companion for KDE, but alas, GNOME apps use ESD (which bypasses Jack) or Pulseaudio (which can direct sound to Jack, but the implementation is flawed in Ubuntu).
It's time for Ubuntu to use its might to blur the barriers between GNOME and KDE worlds, doing away with any technology designed to lock you in one side or another. Unity, despite all its errors, may be a first step in that direction.