First of all, the salesperson (Pierre) was very knowledgeable and was able to answer all our concerns and even point out problems in our current installation.
The installers came at 7am and the crew worked very efficiently. By 8:30am they're already done removing the old shingles, and started laying membranes etc. By 3pm the work is complete, and they made sure all the nails and dusts are cleared all around the house. The house went through some heavy pounding but yet everything still seems to hold (more or less) -- we had a bit of tiny debris in the house due to blowing around the skylights. We wished that they had warned us about this beforehand.
While it's too early to tell whether there'll be problems, but the installers assured us that all the caulking is done. Anyway there is lifetime warranty on the shingles so we should be good.