Before someone here reinvents
http://www.bitcoinplus.com, he might give a try to the original.
I am using it on a few low traffic blogs, and it is not intrusive at all, since it runs at low priority. But in about 3 months made me 0,003 BTC, since cpu mining with javascript is efficient like sh*t.
And that's the reason javascript miners for btc are plain stupid, so hosting websites and put a javascript miner on them will never be enough to cover the costs.
A javascriptminer for litecoin would probably be a whole different story.