Exchange 5.5 vs 2000

After doing some research on the new version of Exchange, and pouring over the documentation for 5.5, it seems that there isn’t much the new 2000 version can do that 5.5 can’t. Is this the case? If so, why not stick w/ 5.5, at least for a few more years?

If I may, one more point of clarification: Can OWA be used w/ 5.5 (and Public Folders?) to allow GroupSharing of documents (Word, Excel, Power Point, etc) over the internet? If so, then I think I know which server to install!