Whether it will actually speed up your connection probably depends on what you'll be doing. For online gaming, it probably wouldn't decrease your ping times - but most likely not possible with most games since you would be sending traffic over more than one IP address. The largest speed increase would probably be with downloading large files. With a 100mb connection you're probably more limited based on the speed of the sites that you are connecting to.

If both 100mb connections were from different ISPs, with different backbone providers, it would be possible with the right hardware to setup a network to use both connections in such a way that traffic is routed over the connection with the most efficient/fastest path to the destination.