Although I see from the popularity statistics that
Jenna had a big surge in popularity starting in 1984 and lasting until pretty recently, to me it still doesn't have the same dated feel as
Jennifer, possibly because I've known quite a few Jennifers and have never known a
Jenna. I like
Jenna much more than
Jennifer, because the part of
Jennifer that I don't like is the "fer" ending, and
Jenna obviously escapes that. I like
Jenna, but even though it personally doesn't sound dated to me, based upon the statistics, I'd advise anyone who wants to escape a popular or soon-to-be dated name to avoid it.