a global recession could slow the market a bit, but people love going online and it's one of the last things they'll give up. so in a recession a company would still have to focus on it's online strategy and companies would still need domains. people might travel less or eat out less to cut back, but they'll still be going online and surfing the net, and that's how companies will reach them.
also consider that many countries still don't have high internet penetration like US, Canada, England, Germany, etc. there are still a lot of people coming online. look at Brazil, China, Russia, etc.
if a new system was found to make domains less relevant, that could bring down the market, but so far there's no sign of that. domains are needed for the web like phone numbers for the telephone.
also, if advertising money stopped moving online (away from traditional media) that would slow things - advertising money is what's driving the whole market and all indications are that money will keep increasing.
As long as the internet stays popular and companies want to advertise online, domain values will hold well. There is still so much more to come in ways to make money from domains, it's exciting!
