That of course is assuming that youir ISP's DNS server is the cause of the problem, which,
tbh, is unlikely. Personally I have found open DNS to be slower in resonse than my ISP's DNS, slower to update, and sometimes doesn't resolve sites that I know exist. For those of us in the UK, why query a server 8,000 miles away in california, when your ISP's is likely to be less than 500 miles away? And acess to your ISP's DNS server is restricted (generally) to the ISP's customer base, while Open DNS servers are accessible by anyone, so performance may be variable anyway.
Open DNS does have its uses, but certainly shouldn't be seen as a panacea for all speed problems.