Leave the leaves. Think of it this way. Did anyone remove the leaves last year? Were the plants healthy. Leaves contain minerals that are used to build the soil as they decompose.

The leaves are generally good for woodland plants - woodland plants have grown for eons being covered with leaves. The only exception is that there may be a few spots in the yard where leaves build up much deeper than average - a low spot in the woods, up against a log where the wind pushes leaves, etc. These areas may accumulate too many leaves for most woodland plants to grow, and you'll find similar places in any natural woodland. It is unlikely plants are growing in such spots, but if you want to encourage new plants, spread the leaves out of the low spot when spring approaches. Generally though, the leaves should stay, and you might even add more in some places.