Random loot scaling is pretty ok - quality of some stuff goes up as one levels up, but lower level items are still present so it´s not like suddenly all minor magicka potions become major ones, etc.
If there´s any hand placed non-quest related loot somewhere, I´ve yet to find some - so far, unfortunately, delving into dungeons I´ve found on my own only netted random, level scaled finds, at least as far as I can tell. Difficulty of locks doesn´t seem to scale (fortunately) and in the context of this it sometimes leads to "inappropriate" results, like opening a master lock and getting 7 gold + petty soul gem. All non-random loot seemed to be quest specific so far.
Rewards from the "radiant" quests are scaled as well, which makes sense because otherwise doing these at higher levels would be worthless. However, other than pointing players to some places, these are still pretty much expandable and only clutter the experience in my opinion (and don´t work optimally - one of these I´ve received pointed me to a dungeon I´ve already been to and upon returning there it was respawned with same mobs, including the named one whose killing was the objective of the first quest I´ve done there).
When it comes to enemies, generally the system is very good for this type of a game. Trash mobs get some higher level enemies added into the mix as one levels up, but similarly as in the case of random loot, weaker ones are still present. This goes both for dungeon and wilderness areas.
There are also encounters which I think are always supposed to be at higher level than player, as in, an encounter nets a draugr overlord at level 12, but draugr deathlord at level 20, etc. Besides the named bosses and such which are set (but very likely scaled as well), there seem to be some static "no-name" encounters too (like the frost troll on a way to Hrothgar, or passive entities, giants and mammoths included).
Dragons, again, follow the similar principle as random loot.
Average level of enemies differs per area, so it´s possible to stumble upon a dungeon where even the weakest foe can mop the floor with a player of lower level.
While I think this in general is a pretty ideal set up, quite often those higher level mobs that get added later seem to be somewhat overkill in the amount of hitpoints they have and damage they can dish - basically, they don´t follow the same rules as players.
Bandits don´t suddenly start wear glass armor, but some of them can still kill my level 31 character in two hits, while I need a lot more to kill them, and they don´t have any special equipment either.
Since I´m playing a jack of all trades character I can´t be sure about that, but my impression is that this may become a problem for pure or "purer" spellcaster builds, because there´s no way to increase damage output of the spells and higher level spells are quite costly to cast (while increasing damage output of weapons is possible).
I´m playing on master difficulty so the above is no doubt exaggerated compared to normal setting, but in principle this is a likely flaw anyway as the mechanics seem to be putting spellcasters in a rather significantly disadvantageous position.