We speak to a wide variety of Internet companies, and it seems that the state of dial-up users is dependent on both the company which you work for and its target market. There is no debate that broadband usage has exploded and continues to grow among users with the financial and infrastructural means to make the leap. Broadband usage in the US has now reached levels over 82% (see www.websiteoptimization.com/bw). However, the death of the dial-up connection may be over-stated. We still have customers with a high percentage of their customer base using dial-up connections and they will remain that way for a long time to come.
From the market trends that we see, the answer to the question of 'should you still care about monitoring and optimizing website performance for dial-up customers?', is yes you still need to care. The only exception to this would be if your application is broadband specific (e.g. if you're key competency is streaming television programs over the Internet, then your business model has most likely decided to forgo those customers who use dial up connections). For the rest of the web applications out there, optimizing for dial-up end-user performance is still crucial as a significant portion of customers and end-users still rely on these slower connections.
To optimize an application for dial-up users it is vital that you first measure your performance from dial-up locations. As the old motto goes, as I remember it, 'you can't manage'(and therefore optimize) what you can't measure'. If you are a current user of Gomez Last Mile Monitoring, then you have access to application monitoring from actual dial-up (Legacy/Saturated G0 ) user desktops and can get insight into your application's performance from the dial-up perspective. Using that detailed insight you can then tune the application using tips and tricks that you may know, or may need to engage with professionals, to perform optimally for all end-users.. Dial-up users are in a sense the least common denominator for performance, so if dial-up users are an important user segment for your application then it is critical to optimize the performance of your site for those users. As for being realistic, yes it is very realistic to do so cost effectively. There are several simple tricks (as well as some more complicated and time-consuming ones) that you can do to speed up performance for your dial-up customers.