In the age of the search engine, my naming advice: make sure people can search for your product. That means don't use a common word (you have to compete with all the pages already using it): Word, Excel, Windows, Apple, Office, Backpack, Ask, Live. Don't use a misspelled common word (users, upon hearing the name, will not know how to spell your variant): Novell, Digg, Topix, Froogle. Don't use capitalization or punctuation to stand out (search engines and search engine users often ignore capitalization and punctuation): C#, .NET, del.icio.us. Don't use names that aren't even in Unicode (the artist formerly known as "the artist formerly known as Prince"). It's okay but not great to use a common word that isn't commonly used on the web: Amazon, Dell, Ta-Da, Macintosh, Mac, Safari, Basecamp. It is fine to use misspellings of uncommon words, but you need to make sure people learn to use your spelling: Google, Flickr. It's better to use two easily spelled words mashed together: PlayStation, MicroSoft, WordPerfect, SketchUp, HotMail, FireFox; or to attach a short distinguishing mark to a common word: eBay, 43Things, GMail, 3Com, iPod, XBox, 30Boxes, 37Signals. If you're going to come up with a brand new word, make sure it's easy to spell once you hear it: Netscape, Akamai, Comcast, Honda, Lego. Don't use a name that's a subset of another name unless the product is a variant of the shorter name: Mac Pro, MacBook, MacBook Pro.
Don't pick a name like Zune unless you have enough marketing muscle to teach everyone that it's Zune, not Zoon. Try searching for
zoon and see what you get. As of this post, the first page of search results doesn't mention Microsoft Zune at all. Every search for
zoon is a lost chance to get a customer.
Many of the above names succeeded despite being bad because they got started before the web became big. But if you're starting a brand new product and call it "Word", I think you'll be shooting yourself in the foot. If you make it hard for people to find you, you'll have fewer customers and you'll make it hard to get the network effects that would bring in even more customers.
It would be interesting to see if there's a correlation between names and popularity, but it would probably be impossible to study this without examining parallel universes.