MacPorts works GREAT for me. No problems at all. I currently use it with a 10.5.8 PPC system, and will continue using it when I upgrade to a 10.6.x Intel. MacPorts is also a lifesaver. As a simple example, I just used it to compile the latest bug-fix release of the VideoLAN media player (VLC 1.0.6), which is currently only available in source form. Without MacPorts, I would need to download and compile by hand, and who knows what would have happened. As it is, I just typed "sudo port install vlc", and MacPorts handled the rest, compiling not only VLC, but all the dependencies, and it used the right variants so that I ended up with a clickable program in my /Applications/MacPorts directory as well. Sweet.
Although I use MacPorts as my primary package manager, I also use Fink, and if you configure things correctly, they can easily co-exist on the same system and not get in each other's way. All you have to do is make sure that the path to MacPorts' directories come before Fink. You do that like this in your .profile or .bash_profile:
test -r /sw/bin/init.sh && . /sw/bin/init.sh