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It's a good material, but it clogs your nozzles really easily. Basically it produces an oily residue as it prints, which eventually accumulates, this may or may not be what forms crusty carbonized deposits inside the heatblock between the nozzle and heatbreak and general vicinity.
Essentially you need to keep an eye on prints and don't just assume they will continue without suddenly clogging.
If you print more or less continuously without letting the nozzle cool down between prints you will probably get flawless performance until the spool finishes and you have to cool the nozzle.
It's not too hard to clean out once clogged, you essentially burn the bejesus out of it with something like a butane torch... outside... becasue it stinks and PET isnt that good for you. You generally want to ventilate while its printing too, its a relatively pleasant smell but it isn't really good for you.
Bed adhesion is quite good, on the right temperature bed.
You don't really need an enclosure for ambient heat control like ABS, but it would totally help.
It's a nice hard material, and pretty. Better than ABS for almost everything, but a bit of a bitch to use, like ABS, but less so.

Have some spare hotends (nozzle, heatblock, heatbreak pipe, and maybe heatsinks on hand.. becasue most of the time it's easier to swap it out and worry about cleaning it all later. iirc it's soluable in the right solvents... but youd need to look that up, and burning it off and wire brushing the components afterwards is much more direct.
Also a nozzle drill/cleaner for your diameter nozzle will be useful.

TL;DR: print.. and don't stop printing.
PS; if your heatbreak pipe has a PTFE/teflon liner (i3 megas do), then beware the ~250C plasticity point, above which you may end up damaging it and getting a fairly serious clog or just an ongoing issue that can be hard ot identify.

2017-10-20 EDIT:
Most of my comments are probably biassed by the fact that I had a damaged ptfe insert, which was causing a partial blockage. Since then I have switched between pla and petg a few times with no issues and without changing nozzles.