In most of the 2011 NFL mock drafts that have come out since the conclusion of the NFL Combine, the Detroit Lions are predicted to select USC offensive tackle Tyron Smith. I'm not quite sure why he has become the name for the Lions in mock drafts, but that is the new trend for Detroit. SB Nation's 2011 NFL mock draft had Smith going to the Lions last week and this week, and now Mel Kiper has the same thing happening in his new mock draft.
Kiper's explanation for the pick is this: The Lions have a need at cornerback. The problem is no cornerbacks worth the 13th overall pick will be available. This means that unless they trade down, a cornerback is unlikely to be their pick in the first round.
This leaves the offensive line as an area in need of improvement. Kiper thinks protecting Matthew Stafford is a key going forward, and Smith is a guy that "has added necessary bulk without losing much in the way of athleticism," and he is a potential long-term solution for the Lions at left tackle.
Kiper's previous mock draft had the Lions taking Colorado cornerback Jimmy Smith. The general consensus is that for a variety of reasons, including off the field stuff, Smith is not worth the 13th overall pick. That is reflected in Kiper's new mock draft, as Smith isn't predicted to be taken until the 26th overall pick (by the Baltimore Ravens).