It depends entirely on your competitors, the importance of speed to your users and the costs involved. If your users are doing any click and trade type stuff o

It depends entirely on your competitors, the importance of speed to your users and the costs involved. If your users are doing any click and trade type stuff or buying and selling products where prices fluctuate over the course of seconds then latency will be a very big issue for them. If on the other hand users are just generally logging in, checking stuff, making payments etc. then latency becomes less of an issue. As a general rule of thumb, make sure that your page shouldn't take more than a few seconds to load on a DSL connection. Any more than 5 seconds and you're going to get frustrated users. You can help by using CDNs to cache static content and making sure your pages are served compressed.