I currently have a Young's Double Chocolate Stout clone (extract & specialty grains) in the primary. I got the recipe from one of the responses to this forum question. (You have to be logged in to beeradvocate to see the responses.)
It's been fermenting for 11 days. Since about day 6 when airlock activity slowed dramatically, there has been a gooey yellow-white film on top of the beer that is holding some bubbles trapped underneath. This film doesn't look like any infections I've ever seen pictures of; it's not fuzzy or crackled and there are no radial patterns laying on top. I don't think it's infected, but I've never seen anything like this in the dozens of batches I've ever made. I think it may be yeast and/or lactose trapped on top of maybe some protein film.
This is the first time I've used lactose (12 ounces of it), cane sugar (4 oz), invert sugar (8 oz), and yeast nutrient (1/8 tsp). If you have experience with any of these ingredients, have you noticed interesting krausen after fermentation slowed similar to what I've described?