I just wanted to discuss the problems concerning customizations and extensions concerning the outlook client in general and the offline client specifically.
When customizing CRM there are many different customization points, among the most important, callouts, or Business Logic Extension. These will work well on the desktop version of the Outlook client since it comunicates directly with the CRM server, in more or less the same way that the web client does. Please note my previous postings concerning how to handle the problem of the "Settings" menu, disapearing from the web-menu. In short, install the Outlook client to one URL and use the webclient on another, and your problem will be solved. It is due to caching problems in IE.
However, when using the laptop client in offline mode, all logic is handled in the client and the callouts are not run, as far as I know, not even when syncronization is done.
Concerning custom aspx-pages on a separate website, it might be possible to create a new site locally on the offline computer and let Casini handle that aswell, and the have special tags in sitemap and isv.config to handle the offline functionality. The webservice won't be available, so I don't know how much functionality you can really create. Perhaps, you can temporarily store some information and connect to the webservice when syncronization is done when the CRM-client goes online. How to connect to this and trigger it, I don't know.
In conclusion, I would like to suggest that you thouroghly revise each customization from the offline perspective and decide how to implement, block or leave out some funtionality on the offline client. To avoid problems with the customer, I would also suggest dealing with this at an early stage in the project.
CRM and SharePoint Consultant