There are presently no patterns, plans, or formulas that require skill beyond 300 to learn and produce. It is unlikely this will ever change. There is a vast difference in quality of items that can be made at 300 though. Some 300 patterns are incredible (but also incredibly rare to reflect that, with very rare/expensive reagents).
Some exceptions: Fishing in very high level zones sometimes requires around 400 fishing skill. 300 is the skill cap, but with bait, rod, and glove enchantment, it is easy to boost your skill +100 or more.
Skinning is capped at 300 like anything else, but that means you can only skin up to L60 mobs (every 5 skill = 1 level higher mob you can skin). Presently, the highest level mobs are L63. So to skin them you're going to need a boost, as previously mentioned. Finkle's Skinner, and the +5 glove enchant are the only ways to go beyond 300.