There is an interesting discussion going on at Webmasterworld on this topic.
One person had this to say:
Currently, online marketing only accounts for around 10% of all advertsing expenditure. Within the next 10 years, that figure will be around 50% if not more. The future is rosy. The people who are looking to make a living online now will benefit more than those who make a start in years to come.
I have been working on the internet for more than a year now, and I have been able to grow my income slowly overtime. Adsense is up and down, but I have been able to diversify into other programs.
If was to take it more seriously and run it as a business, I cannot see any reason, why I couldn’t do this full-time.
I thought that maybe I was late to get in, but I think that maybe there has been no better time to start.