The load time is mostly dependant on latency (ping time) to the database server, not bandwidth.
For some reason the Enterprise Manager basically requests all the database information 1 database at a time instead of in bulk.
On a LAN this isn't so much of a problem, but on long distance connections it can have disastrous results like this.
From the times I have observed it's actually even worse and the program seems to make multiple roundtrips to get all information on a database.
Let's assume you have a 300ms ping time because you're in Australia, and that every database causes 3 requests for information from the Manager client. Now there's also 300'ish databases on the server, so the minimal theoretical time it would take to load the entire list (assuming infinite bandwidth and program response speeds) would be: 300*3*300 = 270,000ms = 4,5 minutes.
I don't have any actual numbers, but as you can see this can quickly amount to long response times, while the same data exchange could theoretically be done within a second on a broadband line if only it was done in bulk.
Basically the Enterprise Manager is not designed to work over an internet connection. Loading only the databases one actually has access to would be very helpful without requiring a large rewrite of any of the software, but it's not gonna happen
SQL Server 2005 is in beta at the moment, perhaps that will improve things eventually. From the feature list I understand the management tools have been changed rather extensively.