For those reporting severe lag when viewing back from the bridge to the Left Rear of the sub 190 to 230 degree position. I get this consistantly near times of changing lighting conditions (screen flashes for an instant.) Rotating the view away or changing view station completely will clear the lag.
List of consistant possible bug feature reports so far (not in order of importance

Note: I've seen these reported by a large number of people so "looks" like game design rather than hardware/user anomily...
1) "Out of air" message when air pressure is replenished.
2) Ghost Bridge crew (solid and normal otherwise.) Feature to assist player awareness?
3) Large frame rate hit viewing certain directions own sub external and bridge.
4) A key CTD.
5) Radar disabled. Related, but appears to be some port upgrades do not get added (I have been able to add some) but not radar. in damage control screen, added SD radar shows up as "Unpack SD Radar..."
6) Captain log data taking too long to display when large.
Non-bug features (possibly irritating but solvable

1) No or inaccurate range or other data displayed in TDC. Click the status button.
2) DirectX not recognized on install. Some people DO have directx problems that have not been detected prior to installing SH4 because not ALL DX files get used for every game. I for one did not install DX from the SH game installation and had no problem when the game installer ran.
3) I have not been able to reproduce any problem associated with using the stopwatch or the depth gauge. As a further note I have not had ANY CTDs or lockups at all other than the A key.
4) Sonar head not player controllable. Undocumented keys are Home and End.
5) Many graphic anomolies reported by single persons may be graphic hardware-drivers-low memory for settings used.
6) Frame hits with Env and Post process filters. I expect this is why these were selectible options. Use the combo that makes your system perform the best.
7) Repair crew animation in Silent mode. I strongly suspect there is only one set of animations for the repair crew and the intent was to display they were actively on station rather than if they were actually repairing or not.
8) I've not seen any unusual parascope behavior in operation or viewing. Cannot reproduce this problem with PP filters or Env on or off.
9) Ship pitching as if in storm while clear and calm. Cannot reproduce. Hardware Graphics system unable to display weather effects?
10) Sonar doesn't work (no contacts, cannot hear any other ships.) Minimum depth for sonar after the 1.1 patch is 54 feet to get accasional or seldom contacts and 55 feet to get all and consistant contacts. This can be influenced by very bad weather. Being near the surface in a storm or heavy weather will reduce or eliminate distant contacts.
-Pv-