Running off of a 2015 Thinkpad X250, I think screen connecting issues (from me cracking chassis) will make it go kaputt by end of this year. Made good use out of it for VCE though. Content with the purchase. It has a 5200U and makes me sad when loading Facebook and YouTube compared to my computer but it does the job with good battery and nice boot times.
Hooked onto the brand so would love to upgrade to a X1 Carbon or some other overpriced model.
The keyword when considering a laptop (say it with me) is:
CONVENIENCE (for you)
You want to have no qualms about it, the weight should mean it's very convenient to carry about, the boot times good enough so that you can use it for quick things without waiting too long, speed fast enough so you only have to jump onto your desktop beast for graphically intensive things, the keyboard and deck not annoying to your wrist and palms, have no insecurities about using it due to the thinness and aesthetics of your device in the sea of ultra books at school, battery etc.
All the factors should make you want to carry it everywhere and use it especially if you are going to spend big bucks on it or planning on it being your daily driver.
Every increase in price should be an increase in convenience of using the laptop.