Where things fall apart is when you're in larger teams where everyone uses the more common tools on the more common OSes. Collaboration becomes much harder, and there are certain walls you can't cross. The other weak spot is with video editing. There are options, but none of them are as easy to use as the ones you'll find on OSX.
Design requires A LOT of screenshotting, and for that I resorted to building my own workflows [0]. That sort of brings up the major benefit of Linux as a designer. You really do get to build out your "dream" setup, and my Desktop over the years is really customized to the way I work, not the way others work. That's part of the joy of design for me, and while it certainly will limit me to working with Startups or companies that are OK with individuality in workflows, it's provided a level of happiness I wouldn't trade. If anyone is interested, I wrote about my thoughts about using Linux as a designer over here [1].