There isn't actually mouselag in this game. The issue is really due to Unreal Engine, and is something that has been around in the engine about as far as I can remember. There is code in the base engine for something called "Mouse Smoothing" which attempts to interpolate the last location of the mouse pointer to the current location, based on a float variable passed to the algorithm. For some people with low or average mouse resolution, a small to medium value for this option is desireable because it feels a lot smoother. For those with high mouse resolution and a medium to low interpolation rate, this is actually very undesireable.
Instead of tracking the mouse location as it moves, it attempts to interpolate it, which results in "snapping" to the nearest point and thus the feel of jerky movement. If you look at the config file, which is encoded with a binary header, you can see mouse smoothing turned on. In most UE games, the option is given ingame to turn mouse smoothing on or off, but the controls menu in BioShock is surprisingly sparse. Also, because the ini is encoded with binary headers, it's impossible to edit it without decoding and re-encoding the file, which nobody has done yet. In fact, it may even be impossible if the game enforces certain settings upon startup if they differ from the defaults. Overall, I am extremely disappointed that you can't manually edit the config in this game. Presumably, they originally did this to prevent hacking of certain settings in the Xbox 360 version (something I helped do on the last UE3 360 game I worked on) but the reasoning for doing this on the PC absolutely escapes me.
I guarantee it won't take long for someone to release a small program to decompile and recompile the config file after the final release of the game. There are a lot of familiar UE3 options in there that I would like to enable/disable. Sigh.
edit: To those who think this is not UE3, having worked on UE3 I can tell you with 100% certainty that it is indeed UE3. I can't see anyone, under any circumstances, implementing as many UE3 settings as I see in the BioShock config file, over to UE2. It would be far easier, time monetarily-speaking, just to port the game over to UE3. Also, the logo you see when booting up the demo is the UE3 logo. I'm not sure if you can even use that if you're not using a UE3 base.
edit: "Rand" almost certainly refers to Ayn Rand, the author of "Atlas Shrugged," the very basis of the premise behind BioShock. If not, I would guess that it referred to the rand() function, commonly used in many programming languages to generate a random output based on a factor of time. But based on the game's setting, I would take the former guess over the latter.
This comment was edited on Aug 21, 04:46.