Possible reasons for a scientist to be fraudulent is glory and fierce competition (which is usually for jobs and grants).
I like to include 'money' in lists regarding motives for fraud too. There is plenty of that floating about in (certain kinds of) science.
From Gene Expression by Razib Khan who some of you may also know from the old gnxp site or perhaps from his BHTV debate with Eliezer.
Link to original post.