i just got the T440s. i haven't tried everything so i'm still tinkering.
i installed jessie almost immediately. no install issues except some initial uefi bios problems i fixed by turning off the 'secure and signed' software check in the bios.
i have tried most things except suspend and can say all is well - i'm running jessie with gnome3. some getting used to the new touchpad but its ok. the screen at 1080p is simply beautiful.
haven't noticed any heating issues - in fact i don't think the temp has gone above about 60C. i haven't decided what to do with the 16gb ssd drive yet.
its not the cheapest laptop but its my 4th thinkpad and i'm rather happy with the brand even though the new T440 line is quite a departure from the old.
overall i highly recommend it and i'm super pleased. like i said, i have had it for less than a week so i'm still setting it up really but so far so good.
hope this helps