Pros: Array reconstruction works properly. Fast setup and use in simple network. Temperature remains low
Cons: Hardware is good, software could be better. Can't set the SMTP port for notifications.
The bottom line: For home/small networks it's a good choice. May not be as good for fine-grained user management or AD/NIS.
I was looking for a decent RAID-enabled NAS for a small net (one Win-Xp-Pro host, one Linux host and some other "embedded" appliances).

My primary requirement was that it MUST handle a disk failure and reconstruct the RAID array without any problem, allowing me to use the hot-swap feature to replace a disk without switching it off.

Yesterday I put my hands on a Promise NS4300N. I don't care the design, but I found it fairly attractive.
The HD drives are inserted into the NAS by prevoiusly enclosing them into a plastic "drawer". Such a drawer is thin and made of cheap plastic, adequate for the home/soho target of the NS4300N, but not comparable to enterprise class enclosures.
I plugged the ethernet cord, the power cord, powered it up and it booted in a few seconds. Installed the utility CD in the Windows host and set it up according to the instructions. In a few minutes my 160 GB RAID-1 array was operational (there are 2 unused HD bays).

The first thing I did was a firmware upgrade (at the time of this writing: 01.02.0000.05), as suggested by the manual. The firmware is Linux based. I hope future versions of the firmware will include an SSH server too.

My windows network is a Workgroup, not a NT domain. I have no problems at all in accessing data on the drive.
I've also setup an nfs mountpoint on the linux client. It works well too, but I found the share name to be all upper-case, not only the first letters are upper case (as reported by the manual).

The web admin interface is fairly usable but it could have been better localized in Italian (my language) and even in English. While the RAID array settings are well designed, other settings are somewhat lacking. For example, the "Mail Alert" setup is lacking the SMTP port setting, which limits my chances to use popular mail accounts.

But let's come to my primary requirement. I simulated a drive failure in the following way:
1- removed one of the 2 drives from its bay
2- the appliance beeped, leds became orange (except for the good drive's led which remains green)
3- the webmin interface showed the array as "Critical"
4- reinserted the drive into the previous bay
5- The web interface showed the status "Reconstructing"
6- Leds remained orange until the reconstruction ended
7- Reconstruction finished, array operational, leds are all green.

The event was logged.

This is enough for me to give it a good rating as it does its primary function properly.

It took 1h 15m to background-reconstruct the RAID-1 array made of two identical MAXTOR STM3160211AS (160 GB) drives.
During the reconstruction, I was able to read and write data to the share with acceptable responsiveness.

The NAS CPU temperature never went over 37 Celsius degrees, and infact the fan's airflow is always colder than my hands...