Before you read this, understand that I am in no way affiliated with Godaddy or any other domain registrar. About 3 weeks ago I switched one of my client's domains from register.com to godaddy.com. I made ZERO changes to the code, content, or ANYTHING on this site. I went from #9 (averaged there for about 2 months) to #6 last week to #4 this week for a very competitive keyword (19.2 million results). Coincidence?
I would say coincidence, unless register.com was having some technical problems before the switch was made.
There are lots of possible reasons for the improvement, so it's probably a coincidence. But when you made the switch, did you also extend the registration time? Some SEO experts think that sites whose registration is getting close to expiring (say in less than a year) will get a slight penalty in the rankings. So if you extended the registration time, you might have removed this penalty, which could have caused the improvement in the SERPs.
There was no switch in registration time. It was a standard transfer. I'm thinking it must have to do with a technical issue. I switched to godaddy because some days I couldn't access the site. Since then I've had no trouble.
Coincidence ? Nope i would not say, it is just the results of your hard work done. I don't think it should be related anyway to the transfer of the registrar. Apparently Google valued more that site for the given keyword and ranked it higher (or simply a competitor hasn't worked hard enough lately and has drop serps and hence your client has gained higher position).
I would say it is a coincidence. The only you change is a couple of fields in the registry database when you do a registrar transfer. If you don't change the nameservers then there is no impact on the domain.