Looks like I'm in the minority since I find nepomuk super useful. I often search contents of files like pdfs. And the new nepomuk plugin for Amarok is awesome. Who doesn't want the ability to move files around on your computer without breaking your music database? And how about real-time updating of metadata like ratings from various places (like Dolphin and Amarok)?
I'm glad they're trying to work out all the kinks.
I think Nepomuk is an awesome concept, and now it's finally getting fast/stable enough to be of practical use :D . In 4.9 I finally have it turned on with little noticeable impact on my system (~7yr old Pentium D), perhaps in 4.10 I'll be able to update that 'little' to 'no' :p .
Akonadi was the same a year or two ago, I steered well clear of it in versions < 4.8, but with 4.8 and 4.9 I haven't yet had Kontact crash on me.
@all the haters: Yes, new features are often a bit unstable. Yes, KDE seem to make things 'default' before they're ready (but at least let you turn it off). But at least the KDE devs bother to improve things (plasma-desktop, dolphin, rekonq, akonadi) until they work, rather than giving up on them instantly or leaving them broken forever...
All that semantic-desktop stuff... I don't use it, I don't like it. Also file indexing in the past was buggy and slow and ate way too many resources. Improvements are welcome but I still hate these binaries on my disk. And it's hard to build KDE with USE="-semantic-desktop". Something will normally always complain.
I think it needs content-aware indexing, i.e. don't index files that contain no "searchable" information.
My problem is that I sometimes have huge text files floating aroundin my home directory or somewhere. It may be germany.osm, so I would manually exclude *.osm. But then I would do something with it and I would end up with germany.txt and Nepomuk would again index it. Or I end up with somethingbig.json. So nepomuk could recognize that there is no "readable" text (less than X% match any dictionary entries) combined with the fact that the files are several gigabytes in size and not index it.
Though you will understand that I would rather use a past tense. I've used and loved KDE since before 1.0 was out. I was impressed not only as a user, but also as a developer. At the time, design decisions, overall code quality and "user caring" was so high, especially compared to lot of other free software. The only other (Free) project I would dare comparing it was the linux kernel. Then it went wrong and I kept on using it and reporting bugs. Then kde 4 went out and I kept doing so. Then 4.1, then 4.2 and the KDE team kept on focusing on themselves ("us as a communauty") and on adding even more buggy stuff, rather than fixing the mess. Oh, and to keep on arguing that KDE 4.0 was not the failure it was.
I dont remember exactly at which version i gave up, but it was probably 4.4 or 4.5. Since then, I only have to deal with lot of KDE installations on computers all around me, but my own computers dont use it.
My main work with KDE today, is to kill Nepomuk to "fix" those computers, to recommend people not to use anything plasma related, and to be very very sorry for all the problems they report and to which i can't do anything.
I often have to remove all kwin effects, for example. But I agree that this question is tricky and is mostly about graphics drivers support on linux, so I dont complain much about it. I rant a little about enabling it by default even on known-to-be-bad graphic drivers.. but it's rather minor compared to all other huge problems in KDE.
And kwin usually knows about driver bugs: It disables certain features known to be broken with ceratin hardware/driver.
(currently on gnome3 - was sick of solid making my optical drive spin up again and again on every new file dialog&dolphin instance. Just to realise that they finally managed to fix this issue for 4.10 - if you use the udisks2-backend...
This bug took YEARS to get fixed, and when it finally was nobody mentioned that in the report...)