Each of my passwords is made up of the same eight-character non-dictionary word, plus the alphabet-position numbers of the first three characters of the name of the site I've made the password for (A -> 1, B -> 2, that old trick).
So for example, say the common word I was using in my passwords was "pizzadog", then my Hacker News password would be "pizzadog813" (H -> 8, A -> 1, C -> 3)
I admit my goal is convenience, as it's clearly only one step up from using the same password for everything, but with the added numbers making me feel a little better in the event of one of them being compromised. But is there any reason why this approach might be considered a bad idea?