I've got two rods, a five and a four, that i've used the shark on for nearly two years. I haven't noticed any grooves in the guides. I fish or guide about 250 days a year. I've caught thousands of fish on these lines and they are still in very good shape, with little cracking or delamination.
I've never had the line burn my finger either. However i have callouses on my hand from stripping line rowing, and shoveling snow, so that helps.
I will never use another rio line. I bought two rio gold lines and they were both total garbage within 45 days. Cracks developed all over the line, little chucks fell off the core and they flat out wouldn't shoot anymore.
I've heard all the bad things people say online about sharksin but that just has not been my personal experience. I will only use sharkskin lines for my personal rods from now on. They are far more durable, float higher, mend easier, shoot farther, and have ZERO memory. Just my opinion.