I'm about 8 months into the BCPNP/PR process.
The PNP application for me took 10 weeks to complete, it can take anywhere up to 13 or 14 weeks apparently.
When you recieve your PNP acceptance if you don't have an existing Visa or you have less than 4 months left on your existing visa then the PNP office will issue you a letter supporting your application for a temporary working visa. This allows you to work for the company sponsoring your PNP while you're waiting for Permanent Residency (PR) to be approved.
When you have this letter you can apply on line for a Visa (current timeline available from CIC website), or you can go to a Canadian border and get your visa at the border immediately (this is what I did). The letter is not a guarantee of a visa it's entirely down to the discretion of the CIC border agent that you're dealing with. The Visa can be for 1, 2 or 3 years, again at the discretion of the border agent. I got a one year visa, a couple of my buddys got 2 years, noone recieved a 3 year visa. The visa only allows you to work in the province and for the company specified on the visa. Any dependents i.e. you hannyangyang
recieve an open work permit, you can work anywhere and for anyone. It costs bout 150$ each for the visas.
This Visa is effectively a bridging visa while you're waiting for CIC to process your permanent residency application. The PR process timeline varies greatly depending on a great number of factors, I'm hoping to get mine in 7 or 8 months. Police Clearance certificates can hold you back significantly timewise as different jurisdictions take varying times to process, you don't need them for your PNP application but you will need them for the PR application so it's worth applying early.
Nominee certificate or the Letter of Acceptance as they are known are not guarantees of acceptance, but it's unlikely you'd be refused and you're PR application is processed significantly faster then other streams.
I don't know how hard it would be to change jobs while waiting for PR approval as I haven't had to. However I do know someone who was able to change employers where the employer was making unreasonable demands of the employee.
O and lastly I'm in Vancouver and it's a great city to live in, though it's terribly expensive
Feel free to PM any other questions
Edit:
Lol while typing Buleg beat me to most of the points I was making above.