The fans had started making some noise, showing signs of giving up. I had long wanted to replace the HD for a bigger one but dreaded what looked like a difficult replace operation. With the fans about to bite the dust, I had the proper motivation to go ahead.
Overall very well. The upper case was the most difficult one to open up. It was a little bent from the years of use and I had to resort to mild violence when prying the front open. I broke a piece of the plastic frame in the process.
Don't hesitate to repair your out of warranty Mac yourself. With the excellent guides from iFixit, you cannot go wrong. And get the spudger! I couldn't have done the repair without it.