6 months ago, I viewed wireless networking as nothing more than a gimmick and dismissed it out of hand, ordering my G4 ibook without it. However I eventually came round to the idea and quickly realised that it takes the laptop idea one step further, enabling you to do "work" anywhere.
So I installed an airport extreme card and a base station a few weeks back and haven't looked back since.
As for as security is concerned, there are a number of things you can do to improve things:
i) don't set the base station to continually broadcast it's presence to the world
ii) enable one of the standard encryption systems on the link (this will come at a the expense of a slight reduction in performance
iii) set the basestation to only accept connections from a predefined list of hardware MAC addresses (these are unique codes assigned to each network card, be it wireless or wired). That means someone else would have to know the MAC address of your card and have card that was able to emulate that address in order to be able to connect. Then the would need to know your password or passphase.
Basically, gen up on the subject before you set things up, apply some common sense and you can't go wrong.
As to whether it is worth the expense or not, well thats for you to decide. Personally, I really like being able to up and move and get a change of scene. I'm looking forward to being able to work in the garden in the summer