You may already know this, but the developers of both Delicious Library and TextMate are going Leopard-only for their version twos.

The DL dev's justification is that almost all the people who spend money on software will buy Apple's stuff first, thus being Leopard-only cuts out only a small amount of your market.

TextMate's dev justified it in a similar way, saying that 90% of his customers are early-adopters who would be on Leopard as soon as it came out.

It is interesting to note that both of these apps have niche markets (people who organise their media collections and programmers/geeks). Thus, the devs are probably confident in their predictions about not reducing their potential customers too much.