Some technical facts about Guild Wars from these three articles:

• Their servers run on blades – originally all IBM, now more varied. Generally these are 2.8 gigahertz dual-processor Xeon IBM blades with 2.5 gigs of RAM.
• There are a number of different categories of servers. These include: Authorization/log-in, game update download, actual gameplay, database cache, DBMS, several secondary game functions (e.g. guild membership, tournaments), and watchdogs overseeing the rest.
• Gameplay servers can support 2500-3500 users each, with the main limitation being addressable memory. (They run on 32-bit Microsoft Windows.) 3500 users is a bit uncomfortable.
• There are 4 ½ million total lines of code.
• Runs on Microsoft SQL Server, mainly Enterprise Edition.
• 1500-2500 transactions/second all day, spiking up to 5000 in their busiest periods.
• They have no full-time DBA (This seems absolutely crazy to me….)

Found via Guild Wars Guru Forums.