Purely my opinion ...as i am one of the march applicants and still waiting..
Less than or approx 50% of the applicants have got IP for March. i would wait this week to hear back from NDVO or atleast till another 5-7 people get IP before starting to get worried.
there is a simple explanation for the delay, "file allocation for various case workers". some are quick - some are a bit drag....hence few of us got delayed...
Main thing they check is file completeness, marraige genuinity and medical. Once case clears this phase it goes through to IP. @ IP stage, background and criminality checks are completed to get to DM.
if you are compelled to do something - you have 3 choices - MP enquiry(usually generic answer " file waiting for intial review"), Case specefic equiry - usually NDVO doesnt reply(but some have got replies), GCMS Notes ( which takes 30 days to get). i have heard from various people GCMS notes helps and sometimes MPs do get some answers.
Hope this helps...