It depends what you need to do with it.
There are some very light ultraportable laptops nowadays, but in most cases maybe a PDA can be enough.
I have just completed a 2 weeks trip, camping out most nights and I used a PDA and a cell phone to check emails, check weather for the next few days and mainly as a GPS navegator (with a bluetooth GPS). This was very handy to go across cities and when I didn´t have a clue where I was and where to go.
Now I am working on a ultralight flexible solar pannel to feed all these toys: PDA, cell phone and GPS