Unless its a Phenom or PhenomII go for the 64 bit. It works great
on my dual core AMD 64 graphics
literally come alive, and the speed is incredible.
I am currently downloading the 32-bit version for the phenom II as
the 64-bit has been quite unsatisfactory. In all fairness it might
just be that machine- its new and was untested previously so am
still experimenting with trying to get it to work properly.

What kind of problems do you have on the Phenom?

I have a Phenom running 64bit 8.10, and I have some problems as well.

The USB ports are intermittent (a reboot always fixes them), the sound
quit and none of the fixes I found with Google work (it works fine
from a live CD), Firefox refuses to download files, and Folding at
Home randomly stops working (I've tried it w/o FAH, in case FAH was
causing some of the other problems, as some people have had trouble
with it, but no improvement).

What i have is the phenom II 920 not sure how much different that is
from yours, but I found the 64 bit OS was a bit much for it ( 4 G of
PC1066) and it can't handle the load. Constantly crashing or
freezing. Video display was very shaky and boot up time was
extremely slow while I had 8.10 on there. So then I switched to
9.04 RC Boot up time was better, but videos were still shakey.
Definitely not capable of multitasking which is what it was supposed
to do best !!!! Currently have a 32 bit Kubuntu 9.04 installed-
not happy with that either altho it did seem to clear up the
resource overload and videos are steady.
Im going back to the Ultimate Edition 2.1 (because thats what Im used
to) but this time with 32 bit - hopefully that will give me a
useable machine. Kubuntu is missing two vital features for me One
is Wine - not even available in the add/remove programs and the other
is DC++ without which I simply cannot function also not available
for download. I started with Gnome and now going back- Kubuntu is
very pretty but not for me. Someday when I can afford more RAM
I might give the 64 bit another go.
Right now I just need to be able to use it.

You've got me thinking ... RAM ... do you have a 4-slot motherboard
with all 4 memory slots populated? If so, this could be related. A lot
of boards have problems with fully populated RAM banks, but AMD-based
ones have always been more notorious for it (as I understand). Could
be that the 64-bit kernel is a little more sensitive to this than the
32-bit. Is your motherboard firmware fully up to date?

Just a thought - might be completely on the wrong track.

4 slots on the MB correct but only 2 are filled for a total of 4G
Ram, its only about a month old
so everything is totally up to date. The onboard video is total crap
- I have a new card to install tomorrow. I redid the OS again
since last post. Now have 32 bit Ultimate Edition 2.1 and its
working quite beautifully. Totally amazing would not recognize it as
the same system. This is doable.
Phenom II's are relatively new on the scene so not much info
available yet. What I can find is simply marketing crap that is not
being verified by what I see.
My dual core is also AMD 64 and its 4 slots are fully populated
with no problems whatsoever and it CAN handle the 64 bit OS- its a
powerhouse ! Unlike the phenom II which is more like the Princess
and the Pea LOL.

OK, you can scratch everything i said about 64 bit on the Phenom II.
The problems were related to the box itself and not to the OS. #1
there was a failing HD being used as the boot drive. #2 the onboard
video was a mess. Both problems have been resolved. Initially I
reloaded the 32 bit ubuntu Intrepid to make sure everything was
working properly before then upgrading to the 64 bit on a
chance. Well this time it has worked, I have a darned nice little
machine here finally. Its stable and fast. Boot up time is a bit
slow but thats inherent with the 8.10 supposedly being aided by
the next version. I will now wait until the official release of 9.04
since its so close to lift off.

For anyone debating on moving up to 64 bit, all I can say is try it
and see. It does seem to boost performance and speed. Graphics of
course are really enhanced. Videos are much sharper and
clearer. Is it necessary ?
No, its not, but if you have the capability - then Why not? Just
make sure you don't have hardware problems- it is super sensitive to
that sort of thing.

Put the 64 bit version on 2 new AMD dual-core machines and works great!

Install the 64 bit adobe flash.
http://labs.adobe.com/technologies/flashplayer10/

The only negative (if it is a negative!) is that there is no 64 bit
adobe reader.