I run Ubuntu 8.04 AM64 on a laptop at work. I’ve been doing this since Ubuntu 6.10. This has not been a smooth ride. Ubuntu 6.10 i386 on my old laptop (I only “upgraded” because the old one was stolen from the plane on a busines trip) worked flawlessly for me. Things have gotten a bit better as upgrades came out, but I still can’t use the wireless (BCM43 device of some sort, no native driver, ndiswrapper won’t play nice), for instance.
My first and biggest tip is to stay away from 64bit linux on the desktop or laptop, unless you know why you need it. That is very unlikely to be the case on laptops.
Moving on, for the longest time Flash would not work. When I tried to configure the nswrapper system, it would start (sometimes) then crash the plugin. Maybe I could view one flash website before needing to restart, maybe no flash web sites. I finally got Flash worked out, and that is the main point of this post.
The trick to make flash work was to first install the 32bit version of FF3 from the Mozilla web site. Put it in a new location (I went with /usr/local/firefox), and put that location in your path before /usr/bin. For this to run, you will need ia32-libs installed.
Step 2 then is to go to the Adobe web and download the Flash 9 .tar.gz. Don’t try to use the autodiscovery/autoinstall thing that Firefox will offer to do. Extract the Flash 9 installer to a temporary directory, then copy the file libflashplayer.so from the temporary directory to the plugins directory (/usr/local/firefox/plugins for me since that is where extracted the 32 bit firefox from the mozilla web site). Now, when you restart firefox, you will be using the 32bit only Flash with a 32bit version of firefox, and everything will work happily.
I think that in general, Linux doesn’t handle the 64bit transition as well as Solaris or Irix did. As far as I can tell, Flash is 32 bit only on all platforms. However on Solaris and Irix, 32bit versions of firefox or Mozilla are supplied, even though they are running on 64bit hardware. Also, there seems to be a lot more of defaulting to 32bit unless specified otherwise, which is often reasonable. And the culter seems to do a better job with supplying both 32bit and 64bit versions of libraries.