Some Karmic applications will work in Lucid. It is hit and miss. Until a
couple of days ago I was using Getdeb repos which only had Karmic releases.
Then they switched to Lucid two days ago. Opera is still for 9.10 and I use
that repository. Some applications will not work because they use older
dependencies and can cause a conflict. Lucid's repos are the same as
Karmic's so an upgrade would upgrade all of the apps as well. Third party
applications may be a problem. You will have to upgrade them separately of
course and you are always taking a risk when you upgrade.

over all it works great for me, yes, some programs don't work, but over all it
works great! Flash, that word is I hate, it seems for me it freezes if you
download flash formats and play in either totem and vlc, however I have not
reported nor comment in launchpad about it.

They fixed Gwibber with a update the other day, had trouble with it using up all
the cpu usage.

But again like I was saying overall it works great! Nice look and feel to it,
and you will like it!

my machine is an amd quad core 4gb ram and 4 hard drives i can run in either 32
bit or 64 bit. in 9.10 its running in 32bit mode when 10.4 comes out if i run in
64 bit mode will the software i'm using in 9.10 still run or does it have to be
64bit software

There is no 10.4, just 10.04. The first number is for the year, 2010 and the
second number is for the fourth month, April (04 not 40). This is the year
and month of release. If you change the numbers you destroy the meaning as
10.10 which comes out next October would have a lower number than the April
release and that does not make sense.

You cannot upgrade from 32 bit to 64-bit. You would have to do a fresh
installation. It is easier than you might think and there are benefits to a
fresh installation. You get a clean slate and you avoid problems that often
accompany upgrades often leftover from old kernels and changes in the OS. In
this case it would likely have to do with the removal of HAL and the
inclusion of Plymouth.

You can backup the list of your applications to a text file and then use it
to reinstall applications. However, you would have to re-download them all.

You should use the 64bit OS if you have 4 GB of Ram. 32bit OS doesn't
address all the memory. (would only see 3 GB)

That was true of linux in the 1990s but modern linux kernels see 4 GB
RAM with no problem.

If you have more than 4 GB, you may benefit from 64 bit OS but the
benefit will probably not be noticeable unless you have a big machine,
e.g. > 8 GB RAM. OTOH application compatibility is known to be better
with 32 bit OSes.