My advice would be:
1) Skip the WiMAX unless you *know* that you have a need for it. WiMAX is a pretty rare thing in most areas, and it's not worth the hardware cost unless you know you're gonna use it.
2) Get the SSD afterwards. You can almost certainly find one cheaper.
3) No comment (no experience.)
4) Get the IPS display. No question.
5) It's generally easier to get the best warranty you can up front (if only because it'll be applied from day 1 as opposed to requiring registration later.)
i've been reading some reviews in other forums (nbr, lenovo) that detail some troubling build quality concerns. lcd bezel deformation, lid separating, palm rest cracks, etc...
Yep. Every ThinkPad in the last ten or so years has had its share of these sorts of posts. I wouldn't read too much into it.
There are ThinkPads which have had real, honest-to-goodness manufacturing or design flaws (the T400s/T410s had a bad palmrest FRU, the T4x tended to die of planar flex, the T3x had failing memory slots, the 600-series had dodgy batteries, etc.), but the X220 really doesn't seem to be one of these. The only real issue of note (IMHO) is the bezel deformation, and that seems to be a cosmetic thing only (and even then, not a guaranteed occurrence.) Personally, I'd get a warranty but I wouldn't be too worried about the X220. If you go by forum posts, every laptop from every brand sucks in every way imaginable.
Need help with Linux or FreeBSD? Catch me on IRC: I'm ThinkRob on FreeNode and EFnet.
Current laptop: Lenovo ThinkPad T420 (running Debian Wheezy) - kestrel [pending retirement]
Current workstation: IBM Intellistation 9228 (running FreeBSD 9.1) - blackbird