We are currently having two UI design for internet and intranet the underlying reason being is that they both serve different purpose so they have different UI design.
But however users want to have a more synchronized look and feel between internet and intranet.
What are the reasons you all can think of in have different user interface/outlook for internet and intranet?
There may be more information available on intranet. Also the tone of the message might be targeted differently but you'd want to ask marketer about that. There might be less of a "sell" to the intranet.
Often authentication would be different and even integrated with domain.
Big difference for intranet is that often you don't need to design to the lowest common denomitor, i.e. what works across many browsers. You might even be able to presume other things about the user's environment you would never be able to on the internet, therefore being able to develop against a known target. Example, you might be able to assume every user runs linux, FF 3 and has flash or alternatively windows vista, IE8 and silverlight.
If the functionality of the two is significantly different, then I believe the UI must also be different.
You can make the two similar by use of colours, menu positioning, themes and so on.
Design budget, the internet facing portal may require more budget to make it look nicer in front of the public audience.
The browsers being to access the web pages may be a reason. While (big) corporate intranets may be Windows dominated and hence Internet Explorer may be a safe assumption to make, out in the (wild,wild) internet, one can't be sure and have to design more inter-operable content.
If the target population is different, you should design your UI accordingly. If the extranet users will not use the intranet, and vice versa, it is natural that the UI is different because business requirements are different.
For instance, extranet could have a more AJAX/web 2.0 oriented design, while intranet users would want focus on the functionality. If you don't need AJAX for intranet, surely the UI implementation will be easier.
On intranets, people tend to share more commercially sensitive information. Therefore keeping the UI slightly different (and distinguished) could help users realise easily that they are in a different area/site.
Another issue is that functionality and use of an intranet is often very different to that of a public website. Public websites are generally geared towards the marketing focus. UI design that aids people in getting a trusted "feel" for the company is important here.
However and intranet is generally much more information dense and can often even be a place to do work. Having a lower marketing type style and instead one which is similar to an application is the key.
Essentially, very different uses leads to different UI designs.
Different users performing different tasks will often need different methods of performing those tasks. That is why they are likely to need different UIs
If the audience and the functionality are the same, you should try to have same UI. If there are technical constraints to have exactly the same UI, you should make sure that it is consistent i.e. both follow the same design principles, where things are, the common workflows work the same route. A user should not have to learn something anew when moving from one interface to other.
Consistent UI is one thing, but there is a difference between the users that should be acknowledged.
Intranet browsing employees has (usually) a pretty clear purpose with their visit, they have also used the website before (and will use it again, whether they like it or not). For intERnet, it might be completely different (depending on you customers). Some might just happen to browse by looking to pick up your products (so selling is a point, which doesn't apply to you employees) as well as the fact that they will not be as skilled in navigating your information. They don't know what's there to find, your employees on the other hand often does. They just need to find 'it'.
Sometimes we will provide a more robust user experience in the intranet site.
For example, we may display a grid of results for a specific business entity, let's say customers.
On the internet site we may only allow the end user to sort the list, using a simple html table to display the results.
While on the intranet site we may use a more robust grid control, in our case the DevExpress grid control, this allows the user to sort, group, filter, and add/remove columns without putting an excessive programming burden on the developer, but delivering a better user experience when it comes to working with the data.
Also, we don't necessarily have the worries as far as bandwidth and page size goes in an intranet site.