Q: Can  more than 1 person use DynamIP on my system?
A: YES. Setup instructions are available here.

Q: Can I post my dynamic IP address to my home page? Should I?
A: YES you can - but NO, you shouldn't.
DynamIP can update almost any web page with the current information and then upload it. Simply add the desired place holders to your web page (e.g. NOT.ON.LINE.NOW for your IP address, etc.) and change the entries for LocalFile and RemoteFile accordingly.
Now, here's why I think that this is not a terribly good idea. Your home page is probably the one page that visitors hit first when they "knock on your door". For that reason you should make sure that your home page is never screwed up. If you use DynamIP to update your IP address on your home page, however, that is exactly what could happen. If anything goes wrong with your upload you'll end up with a scrambled or inaccessible home page (at least until you manage to do a clean upload). Just imagine that your machine crashes at the crucial moment and you can't reboot your thingy for a while, or you have a power outage, <your favorite horror story...>.
It is much safer to use a different page to inform visitors about your dynamic IP address. Link your home page to this separate page and you're all set. If something goes wrong with your upload your home page is still nice and clean and the fact that the page with your dynamic IP address is non-functional probably doesn't matter much if your computer isn't working either.

Q: Uploading the ONline/OFFline files is very slow and fails quite often. What can I do about this?
A: If your trying to upload to a very slow FTP site it is quite possible that the process fails more often than not. You may want to take a closer look at an alternative option called DIPS. Together with DIPS you can serve your ONline/OFFline pages directly from your own computer, i.e. there's nothing to upload. You can read more about DIPS at http://postmodem.com/dips-admin/. Information about how to get DynamIP and DIPS to work together to serve your ONline/OFFline pages from your own machine is available here.