Hi,
I just performed a software upgrade on my ubuntu 6.10 machine. At the end of installation it prompted me that ubuntu 7.04 is also available, but I didn't install it. Because I was not sure if my configuration file remains the same. Most my programs are installed from synaptic repository and only a few of them are installed from source.

I have upgraded my fc3 to fc4 some time back with no change in configuration files.

The only problem I am having with my current version is sound card. Everything was fine with it, until recently when I was playing a sound in xmms. It said that sound card is not configured well. I could play mplayer, xmms and firefox macromedia flash altogether without any problem. Now even I cannot use skype either. All my calls fail, because of some misconfiguration in my sound device.

Do you think it is worth to upgrade my machine to 7.04 or keep the current version?

I would first solve the problems with Edgy before upgrading; the upgrade may not fix them for you. If you feel like it, reinstall the sound-related packages and see if it helps.

The upgrade will ask you, before proceeding, if you want to do the job, and show what packages need to be removed (if any) to accomplish the upgrade. Not necessarily anything, but if a non-Ubuntu-reposity package conflicts, it's removed during the upgrade process. Configuration files may or may not get upgraded/replaced, depending on if they've changed from Edgy to Feisty, but if I remember correctly you are prompted about them too (it may be that you can choose them one by one). At least the old configs should be backed up during the process so nothing is "lost". I did the upgrade myself trough apt/Synaptic and have had no major problems, I recall I just had to reconfigure my locales (I'm not using 100% english) and some language packages.

Fix the sound issues first; Feisty is nice but if your Edgy works fine I don't see no huge reason for an upgrade. If you just feel you'd want something newer, go for it, but fix the sound issues before proceeding. The upgrade process is easy, but if it's interrupted before finishing you may need to run some apt commands manually to finish it (the graphical tool gets fooled if the process is interrupted, and doesn't know how to continue if it goes the bad way), so make sure you don't turn your pc off before all is set

I did the upgrade myself the other day; I can't say it's a much different from Efty. But that's how these things go with such short release-cycles.

b0uncer:
Before reading your comments I performed the upgrade using GUI and unfortunately it couldn't install snmp, snmpd, ubuntu-desktop and some files related hp laser jet printers.
Finally it said that upgrade is aborted and my computer is in unstable state now. Then I rebooted my system to see what really happened, but it never started up again

I did this because of my successful experience of upgrading from fc3 to fc4. I just thought because ubuntu is more stable and it's been 2 years since my first experience, upgrade should be performed smoothly.

Anyways, my problem now is to change grub entries. My linux partition is in /dev/hda2 , but in grub entry, it doesn't show it at all. Instead, it is showing some long hexadecimal values.

Here is my conclusion:
Always install a fresh copy of an operating system instead of upgrading it, even though, you spent a lot of times to configure and customize it according to your needs.

As far ass your sound issue goes, have you tried running alsaconf?

It's better, yes, but I don't see a problem with doing a software upgrade trough a package manager on a desktop pc, because
a) if there is no important information it's all the same if you run into problems and have to do something nasty
b) if there is important information, you have backed it up, right?

Well, enough of that. I didn't have any problems (did that on two machines and done it before to Edgy) and I find it odd that you're unable to boot suddenly. I've done Fedora upgrades too and found them more difficult. But for Grub, did you try to run grub-update (boot using the setup disc), did it help? Or even reinstall Grub completely?

Another thing is that if you do a fresh install, you can always backup the config files you consider important and after the setup compare them with the new originals and overwrite when needed. You may think there are too many of those, but actually it doesn't take you much time to write a small shell script that copies a few "important" system config files and those configs from your home directory that are personal, and after that you can use the script later too.

Also if you run into trouble after an upgrade it's not necessarily wise to boot right afterwards..but then again, how could one know what happens. In what stage did the upgrade process fail? If I'm right, it proceeds somewhat like this:
1) change apt's source list file so that "edgy" reposity names become "feisty"
2) update apt list
3) run a distupgrade, which first downloads and after that installs the packages, doing reconfigurations when needed

Probably the failure came at the "last" stage. You should have tried to update apt's lists again and do a upgrade, possibly with the fix switch, to see if it helped. The upgrade should be safe to do, so it's difficult for me to say what caused your system's failure, but all the same you should be able to fix (or at least try it) a broken upgrade before rebooting..