Baloo has replaced nepomuk and is much better behaved. Akonadi and Telepathy are frequent sources of frustration for me though. Also, the Network Manager can crash all Plasma widgets and window decorations, which is very annoying—I don't know if this is an OpenSuse or KDE bug. As I mentioned a couple months ago (modded +5!), it remains the least annoying DE for me.
I disable both baloo and akonadi (I use no KDE PIM apps). I'm running v5.7.4 on Debian Unstable and telepathy is still busted if you need to connect to a skype for business resource, but perhaps that's fixed in 5.8. Also, I have no love for network manager; my requirements are simple so I use wicd-kde. My Plasma 5 desktop uses about 100MB more RAM at idle than my openbox/compton/tint2/pavucontrol/wicd/conky/pcmanfm desktop did, which means it takes about two seconds longer to boot. But - customizable? I have a desktop service menu with my most-frequently used applications (this was really the only thing I missed from *box) and if one was to look in ~/.config there are enough text files in there to keep me entertained for months.