As you've probably noticed in the other replies here, opinions vary widely :).
These kinds of things are also part of why I switched to OS X in 2003-ish, so I understand the hesitation.
In my experience, Linux is perfectly fine nowadays for these things. I've been traveling a bit recently (and so have been using a lot more random WiFi access points, tethering with my phone, and relying on battery for power), and everything's pretty much just worked for me.
My company's development team is just about 50/50 Linux/Mac now, and I haven't seen any real difference between the two sides with issues for WiFi. In fact, I've probably seen more difficulty on the Mac side recently: I feel like the last few versions of OS X have had the habit of randomly dropping WiFi connections sometimes. One of my friends has an MBP that will drop a connection & refuse to reconnect until restarted (or at least he hasn't yet found a solution that doesn't involve restarting).
It's possible a lot of the issues people report might be down to hardware/distribution choices: not all hardware support is equal, and not all Linux distributions are equal. FWIW I use Arch Linux on a ThinkPad.
That all might sounds a little "works on my machine", but I'm not trying to say that the contrary stories of people having a terrible time aren't valid concerns. What I am saying is that many Linux users have perfectly stable & pleasant experiences, and many Mac/Windows users don't have stable/pleasant experiences, so ultimately YMMV regardless of what setup you choose.