I'm a beginner brewer and I've been doing all grain batches and no kits. I've botched two so far in the recipe stage:
1. This one was a Fat Tire clone type recipe, I found it on Brew365 and on various other forums. The grain bill called for 2 lbs of amber malt in a 5 gallon batch. People said it was a great beer so I brewed it. Well it turns out that the "amber malt" in the recipe wasn't actually an amber malt that you buy at the store, but rather a pale malt that had been toasted in the oven. But being a noob, I wasn't able to deduct anything wrong by looking at the recipe. Its about 6 weeks old now...4 weeks in the bottle and the amber roast smell and taste is so overwhelming that its unpalatable. It may mellow over time, but maybe not.
2. This one was a Belgium type wheat beer recipe that I formulated myself. The grain bill called for 60% pale malt and 40% white wheat malt. For some reason, I left the brew shop with 40% flaked wheat instead of the malted wheat. I basically walked in to the grain room, saw the bin of flaked wheat, and thought "this must be the wheat malt". That was sort of stupid, and I didn't really think about my error until after it was in the fermenter. This one has been in the bottle for 3 weeks and its the best wheat beer I've ever had. I definitely got lucky on this one.
Anyways, some valuable lessons learned along the way. Thought you guys would get a kick out of this