If you are a new user, then you need to be extra cautious about upgrades. I
am not saying not to, but you need to know the inherent risks.

If your old installation works well then you need to ask yourself why would
you want to upgrade? If there are problems already then an upgrade could fix
the problem... or make it worse. It all depends on your situation, hardware,
etc. Experienced users can usually troubleshoot these without a problem, but
new users need help and it can be frustrating for the new users and for the
one helping at a distance.

The biggest problem with 9.04 is the graphics drivers. If you have an Intel
graphics chip, expect to have no desktop effects. If you have ATI then maybe
you could have problems. If you have Nvidia, it will likely work without a
hitch.

The problem is not with 9.04 itself, but the kernel that it uses. The newer
kernel handles some of the graphics chores and makes older drivers obsolete.
Intel knew about this but dragged its feet and users were left in a lurch.
People blame Canonical, but they had little choice in the matter. Everyone
knew the change was coming and there was no problem until it became certain
that Intel would not be forthcoming. They could have put off the release,
but it still is not known when Intel drivers will be available.

People do not realise how complicated a new release can be. You are working
with hardware developers, Xorg, Gnome, KDE and many different projects,
anyone of which can pose a problem for end users.

It is your decision. Just know the risks and be prepared for the
consequences. Back up everything regradless.

As for you menu situation, I would try deleting Menu button and then
re-installing it. Right click, Remove from panel. Then Right-click on empty
panel space, Add to panel.

If that does not work then I would remove all Gnome settings by deleting the
.gnome2 folder in your home folder. Make sure hidden files are enabled under
View.

If that does not work then I would consider re-installing ubuntu-desktop
from synaptic. You can do that by pressing Alt+F2 and typing sudo synaptic
in the box. You do not need to re-install from scratch!