I myself have upgraded my laptop to openSUSE 12.1 RC2 now and I got to see the new Plasma Desktop. Overall, the difference between Tumbleweed and 12.1 are minimal. As expected, considering Tumbleweed (openSUSE's cool rolling release repository) was a hair away from 12.1, the biggest differences are probably artwork and of course Plasma 4.7 instead of 4.6...
KMail2 and Feeding Nepomuk
Ok, there is KMail2 which gave some work. It is really a mixed blessing. A bit slower in opening mails and folders, MUCH faster in checking and downloading new mail (awesome for bad network connections!), painfully big memory usage. There is a problem with the akonadi_nepomuk_email_feeder (yes, feeds mail from Akonadi in Nepomuk for indexing and search) where the queue fills up memory. My 6GB of mail surely doesn't fit in my 2GB ram so that's painful! But it fills up slowly while processing mail so restarting it every 30 min during the night (akonadictl restart) gave it a chance to index all my mails. And this problem is being worked on...Less nice is the constant use of memory (MySQL alone is 120 MB), but I hope there is room to optimize things further. At least it's pretty much stable, which is a bigger deal than memory usage to me. Thanks to Sebastian being supported by donations we have a faster and more stable Nepomuk, making search finally usable for me. Also nice.
Talking about faster and more stable, KWin is noticeably faster again, and blur works great now :D
Other new things
I've also installed the 3rd beta of Calligra which is available from the KDE updated applications repo. It is not perfectly stable (reported my first Tables crash already) but Stage now works with all the standard openSUSE 12.1 presentations, unlike the older KPresenter version. That is good news as it's still quite a bit faster than LibreOffice. Not more stable, yet, both are unfortunately quite crash-happy.I haven't had time to check out Snapper myself, mostly because but I've seen a demo at Brainshare and let's just say I greatly look forward to Desktop Integration! Being able to see previous versions of files and to roll back is really cool, especially once you don't have to go to a separate app anymore but can do it from the file manager.
Played with SAX3 a bit, broke my xorg.conf. Looks like the automatic configuration works better than my manual one...
And yes, systemd boots up marginally faster. And it doesn't seem to break things for me so I'm content with it.
Now, I have to finish some more writing!