I bought the 23861CU with the 1.0Ghz CPU, 20G HD. I boosted memory to 768M (with the special deal on 512M memory) and bought the additional 8-cell battery. I went up to 2 year on site service (and expect my credit card to kick in a third year). I also bought the Backpack Bantam CD RW/DVD-ROM. On my own, I've purchased a 256M USB memory key (for little more than what IBM charges for their 64M key). A separate purchase (I highly recommend) is the Shoreline neoprene cover for 12.1" laptops ($19.99) -- although it's too small when the 8-cell battery is attached.
It's not perfect but I'm quite happy with the machine so far. Mobility and the ease of lugging 2.7 pounds were the most important factors in my purchase. I still find it a little heavy to carry in my shoulder bag along with other necessities. But for regular almost daily lugging, I toss it in my backpack with the neoprene cover and that's fine.
It took a little over a month between ordering and shipping. If you're willing to wait like that you can keep an eye out for special items going on sale. But the IBM sale specialists appear to still be learning about this new system and its accessories -- so do your own research. I had some problems with shipping and returning accessories as a result of poor information. They got resolved satisfactorily upon appeal to a supervisor.
1) I read an online comment that the 20G HD had only 9G left on it. I asked one of the sales reps about this and he told me that I would have 14G on my system (because I wasn't ordering MS Office). Not true. The 20G HD only has about 15G left after partitioning and only about 9G after IBM's installations. I don't have huge space needs and think I can get by with the 9G. But it's a close call and wonder if I'll want to upgrade to 40G eventually.
2) The stick type mouse was almost enough for me to consider returning it. A 1995 Toshiba laptop that I haven't used in ages had one and appears to have given me some carpal tunnel syndrome in the right hand. I was surprised that my first use of the X40 reaggravated that. But with a combination of minimal right hand use, some left-hand use and the use of a USB mouse for prolonged use, I've got it under control. A mouse still seems to be a superior solution in any case. I'm looking into wireless laptop mouse options.
3) I was told by a sales rep that the Backpack Bantam CD would work with the powered USB port. It appears to me that a two prong-type connecting cable is needed for that and it did not come with such a cable.
The final word however is that I'm keeping it and am quite happy with it.