A few days into using KDE3. Here's my opinions.
Overall this desktop kicks ass. It's really really sweet.
Kmail - a lot better than earlier attempts. IMAP actually works, and works well. There are a few wierd bugs - like their filters don't allow you to filter to IMAP server folders. And there is no LDAP support, so I have to use mozilla mail for sending internal emails to people I don't know yet.
Konqueror - A very good browser. Fails to correctly render a few sites (sadly perlmonks home page is one of those). Doesn't support tabbed browsing. But it's nice to have proper KDE integration with it, so I'm giving up hope on tabbed browsing for a little while - so far it's the only real thing I miss from Mozilla.
Noatun - sorry, but this MP3/Ogg player is still far inferior to XMMS.
Kate - this is a really nice editor. With great syntax highlighting, and now has all the features I missed from TextPad, bar one (macros).
Ksirc - still sucks compared to xchat.
Korganizer - nice. Keeps me organised, and integrates nicely with the desktop, alerting me of appointments.
Konq (file manager) - as a file manager Konqueror is actually really nice. The auto-previews are great (but can be turned off) - I find them really useful when searching for source files. Cervisia integration is just incredible - I can totally manage a CVS project from konqueror now, including doing visual merges and diffs, checkins, tagging, etc. Wow.
All in all so far I'm very happy. It's a bit crash happy, but I expect that from this early release, and because of the fact that I'm running a snapshot. Anyway - I recommend it. Try it if you can.