It really depends on what you are making. Big projects (such as Plus!) are best developed with C++ because loads of things are rather low-leveled in C++, compared with VB, and hence programmers needs to do many things themselves, while "molding" all they need, with C++. Still, Cookie is right, VB can actually realize lots of advanced things; if you want to develop a Plus! plugin only, and have just begun to learn VB, just stick to it
It is not that VB is a toy - owing to VB's simplicity and easiness, it's the best programming language to construct many basic, yet essential, programming "concepts/ideas" such as how to best-use a loop, a selecting statement, an array...etc