As posted by others there's no one-size fits all, but it is interesting to see what & how people manage their own stuff, depending on their needs.
My workflow is developing as I use Lightroom more and more, so the below is my LR setup today. I use the term Library, which in LR speak is Catalog; I use one main Catalog for everything.
I start of with 2 main folders - one for Import/Input/Library/Original etc, and one for Export/Output/Product etc. One is for incoming, the other is for outgoing.
Inside both is date ordered by Year then Month then Dated Shoot within each Month.
Dated Shoot means the YYMMDD date code plus a 5 character id code for the shoot, for example 070630-CHOIR or 070712-DAGES. Usually I have an idea of the date I shot something and the shoot code is a visual on what's in the folder. Searching is pretty fast.
In the Output folder each dated shoot has subfolders for final delivery, firstly so I have a copy of everything I've produced and can re-issue if needed, secondly that I usually require delivery for different clients or needs. Examples of subfolders are Media, Client Proof, Client Final, Web Gallery... Metadata, tagging, output resolution etc is usually different for each. I can send a pic to a newspaper a year down the line as I'll still have it with correct copyright info and format (size, resolution, compression etc).
The Library folder has one extra level between the 'Library' and the Year. As my originals can vary, it helps me to distinguish between them by sorting them together. So this level contains Derivatives, Digital, Film, Misc. Derivatives are various images worked elsewhere and imported into the library as an 'original' - or 'base' image - for (further) work/rework. Digital is my main DSLR and hence largest proportion of the Library, Film is scanned 35mm negs/slides and Misc is everything else like p&s snaps or other scanned images sent to me. But inside each of these folders, the Year followed by Month followed by dated shoot code is all the same.
Inside the Library module of Lightroom I use Collections (which I absolutely LOVE! together with the way virtual copies work) to quickly organize images into clients or destinations - one parent Collection is Media, with child collections for each newspaper I send an image to. Another parent is Web Gallery where I put a copy of all images I output for my web gallery (funnily enough). So these Collections are similar to virtual copies of what's in my Output folder, but organized slightly differently.
Hope this helps someone 
"David, what musical instrument do you play?" "I play the Hasselblad!" (David Redfern)