Just shy of seven months after Amazon originally released Kindle for PC, they have released a major update that adds the ability to "create new highlights, notes, and bookmarks and manage those created on your Kindle." This ability was originally released on the Kindle for iPad App, for which search and instant dictionary lookup are also promised to be "coming soon," but no announcement yet if Kindle for PC will get this essential feature. I know that some of the cookbooks I've downloaded are missing linked indexes or a comprehensive table of contents, so without this ability it can be difficult to find a specific recipe (it's often easier to search on the DX, then use the location to find the same place in Kindle for PC).
Other improvements announced: Full screen reading view, color modes, and brightness controls. Again, all features originally introduced with the Kindle for iPad App. I'll admit, the full screen view won't be one I'd be tempted to use on most wide-screen monitors and notebooks these days, but it might work well on a netbook that has the ability to rotate it's display ninety degrees (since Kindle for PC doesn't have this ability, although the iPad does, I suspect due to possible lack of support from the graphics card in most PC's), as that screen would be small enough to comfortably hold and read that way (a 17" widescreen is just to long a line of text for me to be comfortable reading). Still, for some books, I can see that it might allow viewing tables and pictures in a much better size.
Now, all we need is the ability to use the dictionary and perform cross-book searches. Although, I no longer use either function on my original Kindle, as they both became too slow once I had more than a few dozen books; with well over a thousand, either can take 10-15 minutes (or more) to return any answer at all. Adding the ability to print would also be welcome, with, at the least, a 'current view' or 'highlighted text' option, even if it were limited to a small percentage of the book (so you can work off a recipe in the kitchen without worrying about splattering grease or flour on your computer or Kindle). There are, of course, workarounds using screenshots that allow you to get around this restriction, but they are not ones that every computer user might be aware of or feel confident in performing.
If you need help in using the new features, be sure to check the Using Highlights and Notes section of the Kindle for PC's help page, where you'll also find info on the keyboard shortcuts that work inside the application. These can come in handy when reading on a netbook or notebook - turn off the mousepad to save battery power and avoid accidental movements and you can then use the keyboard to completely run the application.