ntfs-3g is hardly a default package in most distros
Actually it's available for over 190 distributions and it's the default one the most popular ones, e.g. Ubuntu, openSUSE, Fedora, Mandriva, Slackware, etc.
Btw, thanks to FUSE, NTFS-3G also works on FreeBSD, NetBSD, OpenSolaris, OS X and some others (more in the way).
NTFS-3G changes rapidly and historically Ubuntu included an old, lower performing version of the NTFS-3G driver. However the one in Ubuntu 8.04 should be ok.
The focus of the NTFS-3G development is reliability and functionality over performance. The performance optimizations started only recently and the current development versions perform close or sometimes surprisingly even better than ext3.
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Actually it's available for over 190 distributions and it's the default one the most popular ones, e.g. Ubuntu, openSUSE, Fedora, Mandriva, Slackware, etc. Btw, thanks to FUSE, NTFS-3G also works on FreeBSD, NetBSD, OpenSolaris, OS X and some others (more in the way).
The reason for the slow NTFS-3G performance on OSX is the use of the incorrect block device. It could be easily fixed but there is no interest for it.
NTFS-3G and all FUSE based file systems support shared-writable mmap
since kernel 2.6.26:
http://ntfs-3g.org/support.html#wine
http://ntfs-3g.org/support.html#vmware
For some reason, when a linux app tries to save a file with a question mark ("?"), which is an INVALID character on Windows
... lose data
No it's NOT invalid. See exlanation at http://ntfs-3g.org/support.html#posixfilenames2
When using characters that have accents on them
Explained at http://ntfs-3g.org/support.html#locale
In all of those cases, the partition works perfectly until you run CHKDSK
Chkdsk never modifies these characters because they are valid (NTFS uses unvalidated UTF16LE).
But most of the performance tricks lose their advantages with FUSE
Why? Current results show that a FUSE file system can be even faster than kernel file systems, e.g. ext3:
Some write speeds from http://www.nabble.com/Re%3A-Porting-Zfs-features-to-ext2-3-p18722897.html
tmpfs: 975 MB/sec
ntfs-3g: 889 MB/sec (note, this FUSE driver is not optimized yet)
ext3: 675 MB/sec
Amarok has a documented performance issue with NTFS-3G: http://ntfs-3g.org/support.html#dd
The NTFS-3G web site has many tips what could be the problem for high CPU usage: http://ntfs-3g.org/support.html#cpu100
Sometimes NTFS defragmentation makes a magic.
The focus of the NTFS-3G development is reliability and functionality over performance. The performance optimizations started only recently and the current development versions perform close or sometimes surprisingly even better than ext3.