I own a large number of domains, currently around 18,500 --but I don't chase specials.
I'll tell you why:
1. It is alot of work to move a large number domains between registrars.
2. The savings are minimal.
3. Sometimes there are restrictions or limitations to the offers. Read carefully!
4. Security and customer service are also very important considerations, and often they are lacking at the companies that make the ostensibly attractive offers.
Check out
www.moniker.com
They are my favorite registrar.