This depends entirely on your community. I know the 0-4 promotion rate in HSL has nose dived in the last few years, followed quickly by the DH screen. I imagine Prowlers have less of this problem since they are sundowning and people are scattering to FAO, IP, etc, other airframes and just getting out completely.
You can go here:
http://www.npc.navy.mil/NR/rdonlyres/0009AF99-9945-4891-AF0A-25C867E2628A/0/FY07USNO4Linestats.pdf
and here:
http://www.npc.navy.mil/NR/rdonlyres/CE42CE6D-095F-45BA-8589-49CB03B8BF25/0/FY08USNO4Linestats.pdf
for 0-4 line select statistics broken down by warfare and community for 07/08respectively.
Take the numbers with a grain of salt though. For example, in 07 there were a total of 110 HSL pilots eligable, above and in zone. 83 were selected, but the summary says a total of 83% selected. Obviously 83 of 110 isn't 83%, its 75%. For comparison, in 05/06 the promote rate was in the high 90s%.
So, at least in HSL/HSM, having a pulse doesn't get you a seat when the music stops, you have to jump for it. EPs in both Sea Tour and Shore Tour help a lot too.