Hi,
The new changes (as told by Fyodor) Nmap dev mailing list

Hi everyone. I spent all day today integrating OS fingerprints, and
managed to get 200 more of your submissions processed. Let's take a
look at how we're doing compared to Nmap OSv1 and other tools:

Synscan (0.1): 25 signatures
SinFP (2.06): 140 signatures
Xprobe2 (0.3): 225 signatures
Nmap Gen2 (4.21ALPHA4): 417 signatures
Nmap Gen1 (4.21ALPHA4): 1,684 signatures

So our signature count is ahead of all the other tools put together,
and we are already to 25% as many sigs as OSv1. Not bad considering
that OSv1 had a 9 year head start!

So I have just released Nmap 4.21ALPHA4 and posted it to the Nmap
download page:

http://insecure.org/nmap/download.html

Please give it a try and let me know quickly if you find any problems!
If all is well tomorrow morning, I plan to put out a release to the
Nmap-hackers. I think this version is better for most people than
4.20 due to the substantial OS detection improvements, and the many
bugfixes. Not to mention the cool experimental features such as NSE
and traceroute.

Here are the changes since ALPHA3:

o Performed another big OS detection run. The DB has grown almost 10%
to 417 fingerprints. All submissions up to February 6 have been
processed. Please keep them coming!

o Fixed XML output so that the opening <os> tag is printed again. The
line which prints this was somehow removed when NSE was integrated.
Thanks to Joshua Abraham for reporting the problem.

o Fixed a small bug in traceroute progress output which didn't
properly indicate completion. [Kris]

o Fixed a portability problem related to the new traceroute
functionality so that it compiles on Mac OS X. Thanks to Christophe
Thil for reporting the problem and sending the 1-line fix.

o Updated nmap-mac-prefixes to include the latest MAC prefix (OUI)
data from the IEEE as of March 20, 2007.

Cheers,
Fyodor
I am particularly impressed to see th -sC switch (nitko signatures)
As of now Nmap 4.21 seems to be stable for me..Any one having any problems with it?