I recently acquired a 'slim' also and I am also concerned about how hot it gets around the side vent, especially when you have the in the vertical position.
Build quality seems better though, feels more solid and less 'creaky' when handling the unit, my main incentive for purchasing the slim was to lower the noise, the slim is still not 'silent' as many people claim, but is is much much better, to be fair the PSU is noisier than the system itself, but not annoyingly so, it's not a whine like my old PSU, but rather a low whooshing sound of air which is much more tolerable and in the day with ambient noise it is practically silent.
I guess we'll just have to see how long these new systems last before I pass full judgement on them.
Also I'm not sure of everyone knows this but the arcade version of the 'slim' will have 4gig internal ram and will be matt rather than gloss, I think I'll grab one of those when there available as I'd prefer matt tbh.