I don't think the desktop is dead yet though, nor will it be in 5 years. I can certainly see a shift in that direction though.
I never said desktop would be dead, it will either just be a smaller player in the number of searches as it won't be the only device a person uses.
When people are searching for stuff at home they'll be using a desktop, laptop, netbook or tablet device and when mobile most likely a smart phone, tablet or netbook.
One report I just read puts iPhone sales alone somewhere around 43M units total and 8M new per quarter. The iPad sold almost 800K units the first month it was released and people expect the numbers to soon be in the millions. Google has put millions of Android phones in the market with Android tablets quickly looming. Microsoft also has lots of Windows phones out there along with Palm, etc. and there are Windows tablets about to launch as well.
So the stark reality is that rapidly almost everyone with a cell phone will have a decent browser available when they upgrade their phone if they didn't already.
If you're sitting at lunch and decide to search for something, do you grab the phone and do it mobile or wait until you get back to the desktop?
Many are doing it mobile, I'm doing it mobile, the wife is doing it mobile, everyone at the bar is clicking on stuff while sipping a pint, it's reached the tipping point (pun intended) IMO already.
Here's a simple example of my problem:
My phone displays AdSense on my site, but the site isn't formatted properly to shove AdSense in your face the same way it does on the desktop. The content the surfer wants is all in a column that you can easily scroll down the phone screen and never see the ads. Sticking ads on the left or right column simply doesn't work because of the dimensions of those little screens. The ads need to be right in the mix with the rest of the data or anchored with CSS so they're always present on the screen.
All I need to do is reformat to make sure the ads are either mixed in with the content or anchored on the screen with CSS, but it's a HUGE site and it's a big job.
However, it's getting to the point it must be done to capture the revenue rapidly being lost otherwise someone else will do it first and make a better mobile experience than my site.