I've just come on to make a comment on how impressed I am that so many P&Q peeps were trying the sewathon.
As someone who does both, I have to say that each discipline has it's own challenges, but in their simplest form it's joining 2 pieces of fabric together. I don't want to come across as patronising but putting a sleeve in, if you use the flat method, which is becoming more and more popular in instructions, is the same as putting two curves together on a quilt.
By the flat method, the sleeve seam and side seam aren't sewn first. The sleeve head is attached to the armsyce, which is just the name given to the curve on the bodice where the sleeve fits, on the flat. This makes it much easier to ease the sleeve head in. You can also clip the curve before insertion by sewing a row of stitching just inside the seam allowance and clipping just up to but not through the stitching. You can also sew French seams, but don't clip the curve. Once it's in, the side seam and sleeve seam is sewn as one.
This method is common for sewing knits, but I have successfully used it on wovens. The only difference on wovens is that I pivot on the seam joining, under the arm, to ensure a more angled seam. Again French seams can be sewn.
Hope that helps. As I said, I don't mean to be patronising, just encouraging