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I've used Xoops for over six years now. There were times I looked elsewhere for a solid CMS to replace it but never went through with it. I never really found anything quite like it.
I find Xoops to be simple enough for someone just starting out while robust and customizable enough for an advanced user. It handles high loads very well. My site now sees about 10k per month in unique visitors. Xoops runs just as well as when I first installed it.
Advanced permissions are another favorite of mine and allow me permission or denial of just about anything, module permissions, blocks, etc.
No one can "sell" you on it but yourself. Do a test install, load up some modules and enjoy. It's a solid system that has more than passed the test of time.