I have debian etch at the moment installed on my slice, stuff seems to be running ok, but it looks like lenny has just been declared stable a few months ago.
Is it time to upgrade my distro? Are there any things I should watch out for?
EDIT
FWIW, I upgraded my web server to lenny yesterday, all is fine. Only caveat was that I had to recompile passenger (a apache mod) because it does not ship as a debian deb.
All settings carried across fine.
I've not done any Etch->Lenny in-place upgrades yet, but if my experience of a number of Woody->Sarge and Sarge->Etch upgrades is anything to go by all is likely to go smoothly and any warnings you need should be given by the package configure scripts as they go on (unless you've changed the prompting options for these on your system.
Having said that: I always take a full backup of the system (i.e. take an image of the system's drives to another machine if you have room somewhere on the network) before attempting the upgrade in case something goes badly wrong, then you can roll back with relative ease.
Also, allow plenty of time. Almost all your installed packages will be upgraded in the "dist-upgrade" step and this will take both time to download, time to unpack, and time to ask you questions were needed. For this reason too make sure that you have a lot for free space, particularly on the partition holding /var/cache where apt will download all the updated packages to during the process.
And make sure you read through the official upgrade document - that will list gotchas known to the release build teams - and don't be tempted to skip or merge steps as the prescribed order will have been tested quite thoroughly and if there was a faster way that was not likely to cause problems anywhere they would probably have found it and included it instead!
If it ain't broken, don't try to fix it. If Etch is supported for some time to come (which I do not know) and you do not specifically need stuff that is only in Lenny, why take the risk of upgrading and possibly breaking your server?
I upgraded to Lenny on my systems within a week of its release, and it went flawlessly. No package breaks, no wierd configuration issues, nothing.
That said, follow the Release Notes for your architecture. It will list common issues and ways around them to make your life easier, should you run into problems.
http://www.debian.org/releases/lenny/releasenotes
If you are just web server (static web page), you are pretty safe. If you got PHPs or Rubies, you should check if the new version compatible.
There is no magic bullet, you have to test your application. Make sure you got backup, just in case.