Is Ubuntu 10.04 a valid replacement for Windows 7 or Mac OS X? Why/Why not?

I'd say that depends on what you plan to do with it and what hardware you plan to run it on. I'm running Ubuntu 10.04 on one of my laptops, an older IBM thinkpad X31 and it's very stable, fast, and has a lot of nice features - mainly the social networking functionality. It's also more.. well, fun, than windows 7. Unfortunately it does have some major flaws in the implementation of suspend/hibernate/resume which have been evident since version 9.10 and have yet to be resolved. If you're planning on running it on a desktop PC then this won't be so much of an issue. Additionally, despite what people may tell you, getting WINE to play with your favourite apps/games is not always as easy as one might hope - and is sometimes downright frustrating, if not unfeasible. Running Windows inside a virtual machine is another option but it kind of defeats the purpose of switching to Linux and you may have problems with applications installed inside the virtual machine. For that reason, I still rely on Windows XP or Windows 7 for anything relating to my work and reserve Linux for the home.

Not for me, Ubuntu is too limited and I see no point to running Ubuntu and Windows 7 in a Virtual Machine when I can just run Windows 7 and do everything in the first place, too what benefit would there be in running Ubuntu as the main OS unless there is a really good reason to.

And WINE can be very troublesome to work correctly.

Too often I would be going, that does not work, cannot download that, well, have to find something else for this main program I would like to use. Makes more sense to stick with something that does 99% of everything.

Why it was not a good replacement for me.

Limited, I could not download any programs I wanted to online, everything takes twice as long to do, the printer, scanner, webcam etc... did not work nor did the software it came with. Extended desktop like Windows uses did not work, could not play for Blu-Ray movies just to name a few. Just not worth all that trouble, yes it does have some nice features yet not enough to use it over Windows 7. As I have said before, I am completely amazed that anyone can use this full time without Windows. I also do not wish to buy for my OS I want my OS to work with what I have and wish to buy.

I'd say yes. I've actually switched from Windows 7 to Ubuntu 10.04. It is a full operating system with plenty of software. If you need Windows software just open a virtual machine.

I agree with cusinndzl, I used to dual boot windows vista with ubuntu 10.04 as the main OS. Best to keep Windows for troubleshooting and troublesome WINE programs.

It all depends on how you go about it.

You can do a lot of things that you might want to be able to do on windows or mac. Some of the software is harder to use than some of the paid for software. But if you work with what you got then you can do pretty much everything.

I've found as a work platform it's perfectly fine. I've had it running as a replacement in the past and I can live with it. But it is a totally different eco system. If you are willing to work with what is there then you might find it does pretty much all you need.

There are even a couple of fun free 3D games, one of which is based on quake 3 and uses cell shading.

Steam is or has been going to be released to work under linux so you will be able to play some, if not all the games from steam.

Right now i'm only using Ubuntu as a server because I have 3 legit XP licenses and one for Windows 7 so right now i've got no reason to change. But it's nice to know that I can easily use Linux if i'm presented with a machine that has it.

yes ubuntu is great even on sub-par hardware but windows tends to be a little sluggish for me and OSX cannot be run easily or legally on a non mac

If you have a Mac, I don't see any point in using Ubuntu over OSX. The only time I would recommend Ubuntu to the average consumer, is if you have an older PC with lower-than-average hardware, or you just can't afford Windows at this time.

Most people will become frustrated trying to find software that they are used to using on Windows. The only good thing about Ubuntu for average consumers, is it is a pretty small learning curve from Windows.

Well first of all, the latest version of Ubuntu 10.10 not 10.04. That aside I think Ubuntu is not a good replacement for Mac OS X or Windows on decent spec. machines. However on older lower Spec. machines that can't run Windows 7 it maybe a good lightweight option. I don't and likely never will use Ubuntu as my main OS but I do have V 10.10 installed in Virtualbox. It is fun to mess around with in a VM but I always want to be able to hit shut down and just use OS X for a while.