I never had a pre-op MRI (other than my diagnostic MRI) but my surgery was done fairly quickly after I was diagnosed. MRI was in mid-April 2007, surgery was 5/31/07.
As for "hardware" - personally I have a lot and I don't notice it at all. In addition to belly fat, I have titanium mesh, a titanium plate & titanium screws - plus I have a titanium rod from my BAHA surgery. All this titanium is in the same area - my BAHA site is directly on top of my AN surgical site - and I don't notice it at all.
Only "issue" I've ever had was a screw (extremely tiny) from my AN surgery that poked through my skin after my BAHA site healed. Removing it was simple - my doc used an extremely screwdriver; took about 5 minutes.
Titanium doesn't beep when you go through airport security, you can still have MRIs, and it doesn't give me any issues in cold weather (I'm in the Chicago area). I'm basically oblivious to it.
Just my experience,
Jan