"Dont try to Buy Domains On Yahoo!" Agreed! It took me one monteh to transfer a domain name from yahoo to other registrar.
Quite to often we forget that Yahoo! and other big names are also run by humans, and just like us, they have their buddies at xxx.com. The rule of thumb is to buy a domain name right away if you think it is good and at least competitive. Switching registrars wont solve your problem. Just buy the domain if it is available.
I've seen the same thing with Network solutions at times too... Now I try to search on a few different ones. Also, try to make it like I'm really into a coming deleted domain name and see if it is picked up (snapped) or goes into auction... I'll try to let someone else fight over the one I don't want... or at least that's what I think I'm doing in my head...