Size of JPG from Photoshop or Pixelmator!
I don't really understand why, but saving out a JPG with Photoshop at "best" quality creates a JPG that is twice the size of a JPG at "best" in Pixelmator. The difference is usually a few kilobytes, but these few kilobytes make a huge difference for your bandwidth usage on the web. It is also very important if you are creating a "mobile" website. I often do work in Photoshop (for flexibility) and reopen and save in Pixelmator to save space. If anyone knows why there is such a big difference between Photoshop and Pixelmator, please post about it in the comments.