First, when I create a new site in iWeb, then publish it to MobileMe, it immediately has an address, regardless of whether that address is reflective of a personal domain name or not. When using Host Excellence, would I need to purchase a new domain name for each individual site)?
No, you don't need to buy a new domain name for each site you create in iWeb. When you sign up at HostExcellence you choose a domain (which is free) like yourdomain.com
To that domain of course you can upload several websites if you want. The addresses of the websites will then result in
and so on...
there's no limit to it.
My iwebfaq.org website is made out of 5 completely separated websites put together to build 1.
iwebfaq.org/site/ (english one)
iwebfaq.org/de/ (german one)
iwebfaq.org/ita/ (italian one)
iwebfaq.org/forum/ (the forum)
Next, just to make sure I'm looking at this accurately, the unlimited web space and data transfer that HE offers relates to the same web-hosting factor that MobileMe's 20GB file storage and 200 GB data transfer applies to, right?
That's right yes. With a normal website you will never use up MobileMe's space and data transfer. You only reach the limit if you have a podcast, huge movies and so on...
Anyway, in using it, have you found any 'catches' to the seeming no-contest situation between these two hosts?
MobileMe's servers are really slow. If I need to upload a 5MB file to my iDisk on MobileMe it takes me half an hour whereas on HE it takes me 5 minutes or less. Also the pages load faster when visiting them.
MobileMe used to be "better" because in IWeb '08 you couldn't publish to a server other than MobileMe's from iWeb itself. From iWeb '09 you can publish to any hosting if you'd like to. I always publish to a folder and upload using another FTP application anyway. Some iWeb features get broken (like comments in Blogs) but there are workarounds or I don't mind of losing them.
The greatest down side of MobileMe is that you can't install a Wordpress blog or a Forum on it and other stuff.
Lastly, it was mentioned in the FAQ that between the Win or Linux options for using HE, Linux is the one to take. Why is that, and would it still be compatible with Windows systems?
Some time ago people reported that they are experiencing some problems (compatibility issues) when storing iWeb websites on Windows hostings/servers. I always used Linux so I can't confirm/deny that. A Linux server is also generally considered to be more stable, safer and faster (whether it's true or not I don't know it's out of my knowledge).
Using a Linux server just means that your website is being stored on a Linux running machine. It doesn't matter at all whether your visitor is running Windows, MacOS or Linux. There are no issues on that side as far as I know.