I've built my own PCs for over 20 years now. Started with a 80286 and built my own and my families' machines until and including today. My last build was a 2600K, a monster of a machine. It's amazing how much computing power we can buy at a very low price compared to the past.
I upgrade in pieces. Oftentimes the CPU is still plenty strong, and a new graphics card will give the system new life. My machines tend to last about 4 years until every part has been replaced.
I can honestly say that SSDs have by far, by very far, been the best thing to happen to a large user base in years. I am an impatient person, and waiting for the hard drive to piece together what the system needs with abysmal access times has bothered me for a long, long time. I've only been able to afford small SSDs, but I will not ever put a system together again that does not boot from a SSD, it would be unthinkable.
4) I am not Canadian.