It all boils down to that what opendns.com can be for you is to function as a backup DNS. It can't in any way improve on the networking itself (e.g. improve routing or reduce hop count, as was suggested earlier in this old thread).

If your ISP has an unreliable DNS then having an alternative ready is of course good, and that's what opendns can give you. However, I would also complain to the ISP..