Pis aren't great as general purpose computers, they aren't powerful enough for that and while they may work (especially with the new, full power Raspberry Pis) they will be pretty sluggish. Besides, if you want a general purpose PC, you could use the money that you would spend on a new Pi and get a much more powerful, used, PC.
The great thing about these devices is to be low cost devices for building projects around. They are cheap, low power (can run on battery if required.etc) and have decent built in I/O (such as the GPIO headers) which are great for connecting to custom hardware.