Adding to secondary is fine. As far as which beer to do it to it really depends. We've put it in just about every beer we make. IPA, Northern English Brown Ale, Double Northern English Brown Ale, Imperial Stout and others. It does different things to different beers. It brings forward grapefruit...
The cedar we use at Cigar City Brewing is cigar box cedar, known as Cedrela or Spanish Cedar. The important thing about it is that it isn't a cedar and it isn't from Spain. It's a mahogany from South America. It does smell a bit like true American cedars, but the flavors it imparts are different.