A few clarifications... some of which have already been made.
Fedora 9 and 10 had ext4... but I think in both, ext4 was optional, took extra work to enable in the installer... and were marked as devel/testing. The same will be true for btrfs.
KDE 4.0 in the initial release of Fedora 9 WAS challenging to use... but Fedora has updated over and over again... following each release of KDE 4 as it happened. Right now 4.1.4 is the latest KDE (except for 4.2 that was just released) and that's what Fedora released packages for about a week ago... for both Fedora 9 and Fedora 10. Will they make KDE 4.2 packages for both? I'm not sure. I wouldn't be surprised if they did.
Here's my experience as a Fedora 9 user:
1) I tried the 4.0 initial release that was included with the install media. I noticed some bugs and everything I noticed had already been reported in bugzilla. At some point I got frustrated and switched to GNOME on one machine and XFCE on another.
2) With each release of KDE 4.0.x and 4.1.x I upgraded Fedora when they released updated packages (usually a couple of weeks after KDE released) and gave KDE a try. Each release had less and less bugs and more and more features.
3) By 4.1.0 I was happy enough to switch back... and I've been using each release of 4.1.x since then... typing this from 4.1.4.
4) While it was an experience perhaps I would have preferred to avoid, it wasn't that painful really... and it did help me become more knowledgeable on GNOME and XFCE. As a result I'd guess that Fedora 9 users may have more experience with multiple desktops and that's not a bad thing. I'd always wanted to give Gnome a try but always found it frustrating but with KDE 4.0's help, I got over that. :)
While people wanting 4.0 in Fedora 9 to be done... no it wasn't... but it did lead to a lot more testing, a lot more bug reports, and a lot more fixes faster as a result. At least I would assume so. It would be interesting if the KDE folks could sort through everything that was reported... sort it out as to where it came from... and figure out how much help Fedora's decision to go to KDE 4.0 only in Fedora 9 actually directly helped KDE. While I don't have any data to support an answer to the question, my guess would be that a significant amount of bug reporting (and probably some code patches/fixes as well from Fedora users and Fedora developers) came out of the Fedora 9 release decision. Was that a concious decision (to help out the KDE folks so much) on Fedora's part? I doubt it.
Did they decide to ship KDE 4.0 just to be cool? I doubt it. I think they were hoping that 4.0 would be completely done and really did not want to dedicate the resources on making two KDE releases in a single distro release (3.5.x and 4.0.x) so they had to make a decision.
Does Fedora pick bleeding edge stuff? In many cases yes, but not on everything. Do they do it to be cool? I don't think so. The Fedora Project has a few properties that people should become aware of if they aren't already... and I'm stating these from experience... and NOT making a statement as a member of the Fedora Project community:
1) Fedora produces a lot of updates. If something is broken, look for an existing bug report and participate. If you can't find one, file a new bug report. Provide information if asked... and become part of the process
2) Fedora likes bleeding edge stuff. What other distro lets you try out the bleeging edge stuff and help in the process as much as Fedora does? While it might not be the distro you give to Grandma (at least not the default install media the first month or two of release) if you want newer stuff, you know where to find it. Fedora is about participation.
3) Fedora moves too fast for most home users. Let's face it, a 6 month release cycle is sorta crazy... from both a developers stand point and from an end users stand point. Why does Fedora do it? Because it is fun... because it is rapid... and because it helps progress the technologies the Fedora Project and Red Hat care about... and that's good for everyone.
Is Fedora right for everyone? Certainly not. Is it right for those who accept the tenants I mention above? Yes, absolutely.
If you want an LTS release, go with Red Hat Enterprise Linux... and if you don't need paid support... feel free to go with CentOS.