Very true I forgot about presence, didn't know about uploading multiple docs!
Having had issues with these when writing a feature that works off the back of upload multiple documents I kind of made it my business to know the libraries that sharepoint uses for office integration. To my knowlege sharepoint registers them from c:\program files\microsoft office\office(xx). where xx is the version number.
using office 2003 components for Stsupld.dll but using the version installed for both name.dll and Owsctl.dll. A common problem when upgrading office versions seems to be features dissapearing, this can usually be fixed by re-registering the 2007 or 2003 version of the required dll based on what features have dissapeared.
It might also be worth mentioning at this point that sharepoint also has a tendancy to work very differently depending on what internet Zone it is in. Put it in the intranet zone in IE and you will be prompted to check a document out or open a read only version in a nice little box... Put it in the trusted sites zone and you will find that the prompt dissapears allowing you to check out with a button from within the office application you are using (regardless of zone settings)... This boils down to seeing how your users are most comfortable using the service, personally we use the intranet zone as imo my users need their hands holding as much as possible.
To the op - what version are you using? there are some neat tricks with WSS 3 (2007) that will give you full fat navigation (as if you had moss) with some small modifications this one change improves usability 10 fold and should be considered at design time. you should also consider where your lists are stored (specifically those that cross reference other lists) as historically sharepoint (wss2 & wss3) have shocking handling of cross site lists (again this can be countered by sensible list locations at design time).
Another thing to mention... on xp clients if you add sharepoint as a network location in the control panel you can then save directly to sharepoint from any office application the below image is the save box for sharepoint 2010 in office 2007:
This same functionality is available in vista and 7 by adding a network location (like a network drive) in my computer.
Basically get it wrong early on and it will make doing the most simple task the biggest of chore, get the design right and it will make the most complex task a plesent stroll in the park
Edit: Just had a look over these posts and noticed we are likely talking about 2010 foundations, like WSS3 the trimmed down navigation model in 2010 foundations will in my opinion be one of the main stumbling points when implimenting a sucessfull sharepoint site. Global navigation (in a form that users will be comfortable with) in foundations 2010 is not really any better than in WSS3 and out of the box in WSS3 it is horrible, in fact it is pretty much non existant both in the user interface and central admin.
If however we are talking the full fat 2010 server then navigation is provided through the publishing infrastructure and global navigation provider which gives security trimmed global navigation for the entire site collection.
I also noticed you work in legal services, depending on your regulation sharepoint can also perform many of the core business functions that are required in a law firm, granted it's not out of the box functionality but we did find that we could for example record times and dates of emails and tie them in with specific cases.
Also what server spec are you looking at running this on? Since our migration (100 odd users 3 alternate access maps) from WSS3 on a 32bit platform to 2010 on a 64bit platform I have noticed that 2010 is a much more resource hungry animal than WSS3. So your looking at a minimum spec of an Xeon Quad, 8-12gb of ram and a raid 5 disk array if you want acceptable performance.
