What kind of laptop you will be happy with is determined by the scope of the work you do. If all you ever do is load RSLinx/Logix5/500/5000 and do ladder then a 1GHz/256MB machine will do.
However the moment you start loading HMI software, SQL stuff, RSNetworx, a drawing package, MSOffice (or OpenOffice which I prefer), browsers, an email client, anti-virus, spyware and a firewall plus a few dozen or more WinXP updates, then after about a six months after you purchased it, your nice new fast laptop will run like an old dog. (I have been there and done this.)
Realistically you want about 2-3 years use out of laptop you have purchased. If after just six months it is already bogged down and sluggish, then at the end of it's life you will truly be cursing the thing. There is nothing worse in any job than having your productivity and mental equilibrium undermined by an unsatisfactory tool.
The fact is that once you buy your PC you have locked in your PC hardware resource for the next 3 years. But in that time the software load on the thing will just keep on growing. Either you buy low cost now and suffer decreasing performance with time, or you buy high price now and loose a lot of depreciation when you do upgrade, (which will still be in about three years time.)
I got my first laptop in 1990, and I am on my seventh one since. This time I got smart and RENTED the sucker. I went out and got the biggest meanest gruntiest Toshiba the shop had.
What I looked for was:
A: 1 GB Ram, 2.4Ghz Processor, 7200 rpm Hard Disk.
B: Built in Wireless, and a Wide Screen.
I twisted on the serial port issue for a while, but I flagged it and I haven't missed it for an instant. I've found with a bit of planning and checking ahead the USB port convertors work just fine. What I do love about this PC is how fast it re-boots, and face it guys we do the "Three Finger Salute" often enough don't we? Yes the 2.4Gig CPU is an overkill for just running RSLogix, but the speed is most valued when I am booting, loading up apps and big files, virus scanning, de-fragging etc.
But the point is this...renting the sucker is costing me a about the same as buying the thing on credit, BUT at the end of 12 months I get to hand it back in and get a nice NEW one with all the latest bells. And the whole thing is tax deductable. The total hit on my bottom line is about the same as buying, but I get to upgrade every 12 months, not every 36 or so.