Encirca is the most reliable .pro registrar but also the most expensive. I haven't had any registration problems with Encirca. The only problem I had was they didn't switch my .pros into my name for the first 2 weeks.
I registered 3 .pros with DomainPeople today, luckily I checked the WHOIS about 10 minutes later because only 1 actually registered. I had to go back and put each domain through individually.
I registered a .pro with DomainPeople on 11 Oct, yesterday, 14 Oct, I get an email saying if I don't email them the last 4 digits of my credit card within 24 hours they will cancel the .pro. It had gone through on the card and I submitted the A/V check.
I have never managed to register a $14.95 with Hostway which is peculiar since they own RegistryPro.
On the first day of relaunch Network Solutions were selling registrations for 3 letter .pros. I regged a few of those and then had to wait a week for a refund.
I regged 6 "o" .pros today with the help of an online crossword puzzle solver;
Apollo.pro
Bravo.pro
Jumbo.pro
Indigo.pro
Pronto.pro
Mango.pro
I thought these short memorable rhyming .pros would be good to have in stock at $19.99 because they work with pretty much any development project. Indigo.pro and Mango.pro would be great for design related sites, Jumbo.pro works for volume discount retail, Pronto.pro has a rhyming "o" and pro in the keyword and would be good for service speed critical sites.
Interesting fact about .pro; there are about 21,000 .pros registered now, up 200% from 8 September, that's about the same as the number of .coms registered at the start of 1993.