Found this very informative information from another thread (from magpie) 
Basically, it describe how CHC and Visa office process an application package. Some information may not be applicable for us. Nonetheless, the information provide answer for probable reasons why some application package take longer than others. Enjoy reading!.. 
Background & Security Checks
Note: Our Background Check comprises of 2 parts:
1. The Standard Documentation Checks,
2. The Security & Criminality Checks.
Standard Documentation Checks:
Our background check is done at the CHC stage. It commences the moment our file gets the 1st BFD by the VO. An indicator of which is the e-CAS that shows "In Progress". All docs been checked & our NOC being tallied against the MI, if the VO finds our case 'eligible' for Canadian PR, the file becomes 'Accepted'; and then it goes for standard background checks, viz. Exp, Quals, Adaptability, Qualitative Considerations etc.
The process involves many things. If our case file is well presented and the enclosures vouch the quality-quantity, adequate POF docs etc., there might not be a requirement of 'actually' calling the employers, references etc. The VOs have a way with that, they are experienced enough to ascertain the logical disposition of our case. But, if there are any concerns of his/her, s/he is likely to ask for additional docs, do further scrutiny vide any means [calling, visiting etc.] & might ask for an Interview.
-Culmination: When 'fully' satisfied, we get the 'Medical Request'.
-Timeframe: Can be anything around 3-8* months, for the 'fast track' system (Avg. 4-5 months).
-eCAS: Continues to Show 'In Process'.
*The older system has a queue, thus can be longer.
Security & Criminality Checks:
A part of the b/ground checks is the 'Security Check'. It commences after our med results are submitted to the CHC. This is a major activity -mainly concerning our 'safe inclusion' into the Canadian Soil; vis-a-vis, Political, Socio-Econmical, Anti-Social disposition, perceived Threat to Canada's integrity etc. This gets us the SDEC, CDEC & SECCRIM.
This is a serious & time-consuming stage, involving many agencies, including CSIS, Interpol, NASC, Database Checking & touch-base with Local Police. Many things are considered here... the No. of countries visited, Applicant coming from 'certain' countries, ex-Servicemen [including Law Enforcement services], Prolonged stay in a country w/out sufficient docs to prove cause, frequent traveling to certain nations, your *Name (?), Inter-Religion/Nationality Marriages etc.
If everything is simple & straight, the file soon gets into the 'final review' stage. If there are any 'red flags', our case goes into a 'spin'. Then our file might go to the local Police/CID agencies; the outcome/timeframe of which is beyond the control of CIC. And thereby the timeframe can be anything [sometimes beyond 1yr]. But, usually this stage should be over by 5 months max. However, a point to be noted is that we can also be called for an Interview [at this stage], due to this reason.
-Culmination: Only upon security clearance we receive the PPR.
-Timeframe: Around 2-6 months. Avg. 3 months. [With new system, sometimes PPR is clubbed with Meds]
-eCAS: Still 'In Process', but 'Med Results Recd.' inside.
The Process in a Nutshell:
Stage-1: [CIO stage] Send Initial Apps+Processing Fees to CIO-NS > Qualitative Check > Issue of AOR+120 days Letter >
Stage-2: [CHC/CIC stage onwards] Send Full Docs+RPRF to the Local Visa Office > File on Queue > e-Cas: "Received by Visa Office" > Eligibility Check+PSDEC > Issue of 2nd AOR > Background Check > Issue of Additional docs Request [if any] > 1st BF'D > e-Cas: "In Process" > Send Addnl. Docs > Issue of Med Request > 2nd BF'D >
Stage-3: Meds Sent > e-Cas: "Medical Results Recd." > Issue of PPR* > Send Passport/s > Security Check > Visa/s Stamped > e-Cas: "Decision Made" >
*The Meds & PPR are sometimes 'clubbed' together.
Stage-4: Return of 'Stamped' Passport/s+COPR > Landing at the POE > e-Cas: "Completed".
Pero ganun talaga.. Sigurado naman mgkakaron ka ng new friends dyan 
