First of all, welcome to the forum.
What do you mean with "my pc slows down"? It's normal that using compiz slows down your netbook a little bit, but it should be barely noticeable. I'm using advanced visual effects (customized through the compizconfig settings manager following my needs) and I get some slowdowns in animations only when my NC10 is under heavy load (for example while handling big files).
Concerning the vanished applets, I don't know what can be the cause... probably restarting the desktop session will restore them.
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