The proportion of submissions to Nature Precedings that are manuscripts appears to be increasing.

From the Wikipedia article on Nature Precedings:

55 preprints were posted in the first 15 days of Nature Precedings. Of these, 26 were submitted as manuscripts and 29 as posters/presentations. Corresponding numbers for the first 50 days are 89, 48 and 41, and for the first six months, 303, 227 and 76.