oh, I would like to share my experience here.

around mid of december 2012, I went for SI (I'm a PETRONAS scholar)
SI result was out around 31st January 2013 (Gotta wait till our final examination result came out)
a week later, 7th February (if Im not mistaken) received a phone call for placement from PETRONAS. (like chitchat session or something)
I was told that the medical check up letter will be emailed after chinese new year.
Due to some graduation problem I received the medical check up letter a bit late than as told. But not that late la. I received it last Monday. (On previous Friday they called me to inform on the kelewatan)

And yesterday I went to PUSRAWI, do all the medical checkup and stuff. At around 3 I sent the result to HRM at KLCC.
And early this morning, I received the offer letter through email (so fast meh! I was so surprised, (iyalah, after reading through this thread))

Oh the conclusion is, I guess HR PETRONAS is not that slow.
Plus if I'm not mistaken, different OPU has their own different HR.

I'll be reporting for duty this coming 1st, March.

and my PIPE will start on 18th March.

p/s: pretty excited to start working at PETRONAS. I'm looking for any kind of guidances and experiences from all of you here. Thank you!

PMU

yup yup. as ixus said, you could call them up to ask for the status of the medical letter.
sometimes, the lateness (does this word exist?) might comes from different source. which in my case, from my university)

and if you live nearby kl, (melaka, seremban, perak etc) you should go to pusrawi for the check up, as they can provide you the result exactly on the same day. (provided tak ramai orang plus you datang pagi)
once you get the result, immediately go to klcc and send the result directly to the hr handling you.