I think overcharging for RAM (or HDD/SSD) upgrades is one way that OEMs make more money off of their machines. I am a bit amused that this is the reason you give for reconsidering Lenovo when Apple (the maker of your current machine) is notorious for doing this: http://www.zdnet.com/blog/hardware/just-whats-so-special-abo...

One good thing about ThinkPads is that most of them do not have their RAM soldered to their motherboards, so it is easy to buy your own RAM on NewEgg and then augment or replace the machine's original memory.

well then i would suggest not buying that model. i keep editing this trying to find a non-snarky way of conveying the following: basically, you do still need to think a little bit. if you want to avoid thinking completely then you probably aren't going to enjoy linux.

in general, thinkpads have good support for linux. i've had various x series laptops over the years and they've been very solid (more so than my partner's macs, where i need to keep replacing fans and power cables).

for desktops, just build what you want. as long as you avoid strange or very new hardware it generally just works.