BrookHarty writes "There is a large number of users reporting nausea while playing Half-Life 2. There is a thread on the Steam powered forums that talks about the wide spread problem. Some other sites are actively talking about the motion sickness, PlanetHalflife, 3DGPU, usenet group comp.sys.ibm.pc.games.action has an active discussion, and gaming IRC network Gamesurge on channel #Halflife2."
In related news from people with too much time on their hands, Jacques Chester writes "Folks discussing the visual merits of the Source and Doom 3 engines might want to look at this. The goal is to see what Half-Life levels might look like in Doom 3. An eerie result."