I'll have to agree with Aenigma. It's a common misconception that coastlines always have to be jagged. There are many, many places in our own world that has long stretches of very smooth coastline. Africa, India, etc etc. The best thing to do is to have some parts that are smooth and others that are more jagged and rough.

One other thing about your coastlines, is that in a couple of places they seem to suffer from a Photoshop clouds issue, which is that the clouds command in PS (and perhaps in some other apps as well) tends to create diagonally oriented landmasses. Now this isn't really a problem except for those of us who notice such things. This is mainly apparent in the south-eastern part of the north-western continent, and in the eastern-most part of the south-central continent. If you wanted you could just change those parts into something more random-looking.

Other than that, what you have so far looks great. And you're obviously putting a lot of detail into the map, considering ocean currents and such. Looking forward to seeing more!