The machines I see on DW20's videos seem overpowered to me, when combined with other mods.
I like the water and leaf blocks, but for example tanks look way too cheap when compared with RailCraft tanks (which basically seem to do the same, but look far less cool).
The automatic transport / sharing of items and liquids between blocks is nice, but transportation generally costs energy (even if the required amount is small enough for a redstone engine). The same holds for the autocrafting.
For example, take the way the bog earth is created in the peat farm. Normally, it would require a carpenter (which eats BC energy and water) and mulch (which requires an extra machine and a steady supply of wheat and seeds) in order to automate this, not to forget the pipes / tubes to connect them. Now it kind of feels like things are created out of nothing. Even a system in which water buckets are used instead of a carpenter would require specialized machines for generating water, getting the water into the bucket, moving the bucket around and crafting the bog earth.
I can think of a few different examples where the shown XyCraft machines give you an unfair (in my opinion) advantage.
Will there at least be an energy network involved with these machines at some point?
Also, I have noticed the corn bug. It happened to me once and I thought in was intentional. It stopped happening though. I may have installed a different version (DW20 pack on FTB) since, or I might just be lucky now (I have not moved my farm). It was really only corn.
EDIT: mutopian may be right. It could be that it has only happened while creating the farm. However, I would expect the seed no to be planted at all (instead of breaking).