Fortune's Pete Lewis says that 802.11g is definitely not ready yet: Pete makes a good case from his experience that current gear needs a little more time in the oven. I've been working with AirPort Extreme and Linksys's 54G equipment, and am not quite as disappointed as him, but I'm expecting less.
Pete does make a statement that I have to object to: 802.11b was ratified several years ago, and yet it's not uncommon for 11b wireless networking products from one company to be incompatible with 11b products from another. There's no reason to believe that 802.11g will be any different.
Later in his blog entry he notes that 802.11b and Wi-Fi aren't interchangeable terms, of course: Wi-Fi means certified interoperable. I don't know of any Wi-Fi equipment that doesn't work with other Wi-Fi equipment, and I'm not sure if he has specific products in mind when he makes that statement.