For me, and I'm currently in Costa Rica, having just driven down from MI. with my laptop, I am very glad I brought it. I have a blogging site going covering the trip and there's just no way I could spend the hours a day I do sometimes after a long day of travel working on my site, setting up dated posts to go out, working with my photo's and doing drafts for future posts on public computers, or where ever I might happen to find them. I was on a schedule travel wise, and I absolutely had no time for searching out places in the dark after a long day of riding.
The other thing is while in the u.s. its great to find a motel chain that has wi-fi, take a day off for rest and working on my site and contacting friends. That luxury was very rare for me since I left Texas. Since I avoid big City's on this trip to save time, the only hotels I found since Texas that had an internet connection was a Comfort Inn in El Salvador, and now a Best Western in Costa Rica. And these chain hotels of course are twice as expensive as anything local, so you pay for the luxury.
A lot of the hotels I stay'd at I was able to plug in to an outlet and take notes on my trip, or set up drafts and I loved that as well. But none of them had any type of connection, one room didn't even have an outlet to charge my battery!
I suppose if you do your home work, speak good Spanish, and are not on too tight of schedule you could line these things up a head of time. But to just go out as I did and expect to run into internet connected hotels and internet cafes as you cross Mexico for your first time isn't realistic. I have a hard enough time trying to find a bank down here! But like I said I am really glad I brought it, there's no way I could monopolize a hotels computer for as long as I use it in my room.