Software developers can easily "export" (i.e., take remote jobs for foreign companies), and a cheaper pound makes them more attractive. I doubt many tech jobs will move to Berlin -- from what I've heard, despite the hype, London's tech scene is much bigger and more developed.

The big threat is from finance. Tech salaries are held up by the huge numbers of devs working for banks, and that would change if there's a major impact to the finance sector. Apparently the City is pretty robust, though, and Euro-related business is only a small amount of their activity.