Lightroom is the way to go. Download the trial and give it a try, though I do recommend reading a bit or watching a few videos first to get the most out of your trial.

Lightroom will let you do whatever you wish on the file system side, and then offer flexibility beyond it. This is important, because this NAS won't be your last, and in fact, you may have more than one eventually. Lightroom does not care where your images are, and even functions with them offline (though not as well).

By arranging things on your harddrive, you are providing information about your images that will be lost when your images are separated from your hardrive, such as posting onto Flickr. The info is useful to you...I do understand that. However, the fact that the image came from "2010/Christmas2010" will not transfer to your Flickr upload, so it is important that you leverage something else, in particular keywords and tags that can be embedded into the image.

You can arrange your photos however you wish on the hard drive (date, event, or one big directory if you wish) and then in Lightroom create collections, tags, keywords and even what are called 'smart collections' that dynamically add images. You can tag images with keywords that will write to EXIF/IPTC, and use Lightroom's filters and search to show you related images. However it can be a bit of a pain to constantly search and filter, so Lightroom offers Collections, which are 'virtual directories' that contain images you have assigned to them. Of course, these have no relation to the actual directories on your hard drive, which is nice...you no longer have to worry about this aspect of organizing. And finally, there are Smart Collections, or virtual directories that are dynamic and automatic, so for example, you can create a Smart Collection based on certain keywords. Every new image with that keyword will be automatically added to the Smart Collection.

I find it helpful to have my images in directories related to year, then by day that I took the image: (2010/2010-12-25), because I recall when I took photos. Lightroom does this for me with its import utility. I simply tell Lightroom how I want to import, and it does automatically every time. Then, I tag images with keywords, typically related to events or subjects. If I have a particular event or project, I will create a collection to make it easy to return to (vs searching or filtering the view). For some items I create smart collections that are dynamic, such as images of family members.

When I upload to Smugmug, all the tags and keywords stay with the image, and they are easy to find on Smugmug as well.

Give Lightroom a try.