Does it generally cause any problems if you want to keep the newest version of a particular piece of software installed on debian stable?

I've read somewhere that using a sid package on debian stable is not a good idea. What about just installing the software manually?

If you want to do this is it just a better idea to "upgrade" your distro from stable to testing, even if it was a production server?

I forgot to add that there are no backports for this package.

If you must have a newer version, upgrading to Testing is an infinitely better idea than adding Sid or Testing packages to Stable. If you do not want to upgrade, but a package is not in backports, you could build it from source. I shall not try to give any specific advice, since I have never tried it. (I have theoretical knowledge, but no practical experience.)

In spite of the name, Debian Testing (Wheezy) is far more stable than even older versions of Ubuntu. Building something from source can be painful because of the dependencies. In other words the libraries which needs to be installed prior to compiling the source.

Regards,
Stefan

Is adding unstable packages to a testing install generally ok?

That seems like the way to go the lib problem seems like it could be a potential nightmare.

If you want to add it, the best way is to use APT preferences. I have used this without to much problems but it has the potential to leave your system in an interesting state. Have a look at this.

You could always try to compile from source in the 1st instance. The degree of a nightmare depends a lot on the package. Once you have decompressed the source file the INSTALL.txt or README.txt lists the requirements, you then run ./configure which will also report missing libraries. If this does not fly, try plan B.

Regards,
Stefan

Pointless thread if you don't state what the package is...?

If you're still running Debian Sarge, then forget about backporting it, you will need to upgrade to at least squeeze.

1 members found this post helpful.

Not only is it ok there is even a name for it. It's called "apt-pinning". You can read about it here. I think you'll find it's quite easy to do.
Have fun,
jdk

1 members found this post helpful.

Caravel also made a good point. Knowing which packages you want to add would allow people to provide more detailed advice. At present, people can only speak in generalities.

Depending on whatever package he/she is trying to install, this could still replace half his/her system with testing/unstable packages.

@the OP

Download/apt-get the source package and build it for your system.

If it needs dependencies that aren't available, consider installing/extracting them manually in /opt and go from there (if really needed, not recommended, difficult to maintain).

Yes! That's possible in theory (e.g. alt-pinning the testing version of kde-full) but highly unlikely. Furthermore aptitude always asks for a verification if what you are doing involves installing more packages than the original command calls for. It also lists all the additional packages it's going to install and waits for you to confirm before going ahead. I wouldn't get my knickers in a twist over it.
jdk

Aptitude also gets stuck in resolving dependency conflicts so it maybe better to use apt-get.

It's never but happened to me and I've been using aptitude for many years. YMMV. If you prefer apt-get, then that's your Stallman-given right to use it.
jdk

While I am generally an apt-get user I feel that I should defend aptitude in this case.

Aptitude actually is better at resolving dependency problems in general. Apt-get will not resolve them except in a very crude way, usually by removing things best left in there.

As most dependency problems do not exist in the APT system anymore if you are using an install that does not have a wild mix of sources this is not a problem with apt-get for most people.

If you are mixing sources in a willy nilly manner, as proposed in this thread, then aptitude is the only tool to be using for all your package management chores in my opinion.

I used to use aptitude faithfully until I tried upgrading from squeeze to wheezy which failed while using aptitude but succeeded using apt-get.

Ah, I understand. I've only ever used aptitude on testing. Perhaps that may explain the difference in our experiences.
ciao,
jdk