The PC version of Call of Duty 4 has a new v1.5 patch, but there are a few gotchas before you run off to get it. First, be sure you've updated to v1.4 first or you won't have the Winter Crash map. And don't update past v1.4 if you still want access to v1.4 servers. Here's what you get if you do update: better server browsing, several improvements for advanced users (for instance, developer script for multiplayer modding) and lots of bug fixes (e.g., the sniper scope steady message only appears when relevant). PS3 and Xbox 360 players can expect improvement soon too in the form of a multiplayer map pack. No word on pricing or release date, just that we'll see them "this spring"...
