This post is being updated with new info when available.
TLDR Average overall input lag from click to screen
Quake Live.
Logitech G100s 14ms (9ms..16ms)
Zowie EC2 CL 28ms (24ms..32ms)
Corsair Vengeance K65 (Cherry Red) 14ms (9ms..16ms)
Razer Blackwidow Tournament (Razer Green) 21ms (17..24ms)
Tesoro Durandal Ultimate (Cherry Red) 16ms (12ms..19ms)

Q3A: Logitech G100s 22ms
CSGO: Logitech G100s 22ms
NEW UT ALPHA (19-08-14 build) @250FPS: Logitech G100s 15ms

For mice button latency comparison see this picture from this blog. Results are relative to G300, mice with negative results are faster than it.

Measurement target.
Measure full input lag for QL/CSGO from click to client side effect appearing on the screen for different hardware setups and software settings.
Measure start motion lag for QL/CSGO from mouse movement start to first reaction on screen appear.

PC: i5 4690, GTX760 Hawk, Z87M Gaming mb, RAM CMZ8GX3M2A1600C8R 2x8Gb, Kingston HyperX 3K SSD.
Monitors: BenQ XL2411T, Sony G520 CRT
Mouse: Zowie EC2 CL and Logitech G100s modded with LED, which is driven by Mouse 1 switch of the mouse directly
actual DPI values zowie 421dpi, g100s 937dpi
using following formula DPI = 360*2,54 / (cm360*m_yaw*QLsensitivity) (source )

Camera: Casio EX-FH25 all filming is done at 1000FPS.

Main measurement.
Vsync always OFF.
CSGO max_fps=250 everything else at default
QL 250FPS com_idlesleep 0 in_mouse 2
LCD 144Hz, 1080p, instand mode on, ama premium, brightness 100%, image mode standard
CPU every setting at default in bios
GPU everything in nvidia driver software set to highest performance and lowest quality
QL ZOWIE EC2 CL Average overall input lag 28ms. Lowest 24ms, highest 32ms. 50+ measurements. Sample VIDEO:
QL Logitech G100s Average overall input lag 14ms. Lowest 9ms, highest 16ms. 30 measurements. Sample VIDEO:
CSGO Logitech G100s Average overall input lag 22ms. Lowest 17ms, highest 25ms. 10 measurements. Sample VIDEO:

Start motion lag test results - 15ms for both Zowie EC2 CL (450 and 2300 CPI) and Logitech G100s (measured for default 1000CPI and 400DPI, non-native DPIs are not adding measurable delay) both of them had lowest value of 10ms and highest of 17ms
same setup as execept I use 144Hz LCD instead of CRT.
Footage example

Other tests and results
CRT result At 144Hz I could not find measurable difference in input lag. At 170Hz input lag tended to be couple ms less. I did not get anything more than 29ms. Lowest was 20ms. 20 measurements.

Things, that do not affect input lag (or their impact is less than 2-3ms). 10 tests for all
1. Maximum prerendered frames setting in nvidia control panel both for QL/CSGO
2. Scaling setting in nvidia control panel. QL
3. Ingame resolution. QL
4. Turning on/off aero. QL
5. GPU scaling. QL
6. Monitor scaling. QL
7. Turbo Boost/C-States/EIST/Thermal Monitor/Etc. QL
8. PEG Gen2/Gen3 Slot Configuration. QL
9. Execute Disable Bit. QL
10. Intel Virtualization Technology. QL
11. xHCI pre-boot driver / xHCI mode / xHCI hand-off. QL
12. eHCI hand-off. QL
13. On-board audio (:D). QL
14. Wake on Lan (:D). QL
15. Java, Flash, IE, Print Spooler, Human Interface Device Access (:D:D:D). QL
16. Turning HPET ON/OFF with command line in Windows 7, while HPET is ON in BIOS. QL/CSGO
17. BenQ overdrive options. QL

Things, that do affect input lag
1. 32ms avg for 125fps (30 measurements). QL
2. HPET OFF = stutters + drops in frame rate + it adds HUGE input lag variace - I made 10 measurements and it was anything from 26ms to 90ms (!!!) turning HPET on/off with cmd in WIndows 7 did not make any difference QL/CSGO
3. Lightboost tends to add couple ms, but since this is within measurement tolerance and I actually need to perform 50+ events checking I got lazy about doing more measurements. QL
4. BenQ built in featrues Aspect, 17" and 19" are all adding 5-8ms. Take a note that those are only available with 120Hz, so it might be partially due to the lower refresh rate. QL
5. Turning off scaling completely in nvidia control panel resulted in ~3ms more input lag, but it might be due to the low amount of measurements. I will perform more for this later. QL
6. Instant mode OFF = +7ms lag to the color state, but grey reponse is still ~28ms QL
Picture for Zowie EC2 CL

Some footages: 51mb 29mb 30mb

Use Media Player Classic Home Cinema (MPC-HC) from to view frame by frame. VLC can do this too.

Win 7 Pro 64bit (with latest updates), Media Player Classic Home Cinema (MPC-HC), Quake Live

Measurement method.
Stick LED to the bottom of the monitor
Load local game in QL
Press mouse 1
Film the process
Count frames between LED fire and first signs of rail trail appear at the bottom region of monitor

Measurement tolerance.
EDIT 18-08-2014
So I performed various expiriments to check stability of framerate of the camera. It turned out to be pretty good. I could not find single inconsistency. So measurment done by frame counting between events has ±1ms (±1 camera frame).
After I have done over 150 measurements overall for mouse1 input lag, I can safely say that 10 measurements is enough to determine this value. Frame length is ~7ms @144Hz, for XL2411T , so depending on input timing we will always get 7ms variance of input lag overall if enough measurements are done. So it will be enough to perform only few measurements (~10) to get good idea what amount of frames it takes to react to mouse click or motion start. However for more or less accurate number we need 50 measurements at least to randomize input time. Currently I do not have neither time nor will to make it THAT accurate for each measurement. However I did perform 50 tests for zowie and 30 tests for g100s mouse1 click latency because that was the most I was interested at. That should be enough, to get a good idea which mouse have significantly more latency.

so I have done input lag test for current build UnrealTournament.exe 19-08-2014 with g100s.
First I did check how it subjectivly feels. It feels good. Input lag (mouse1->first sign of gun shot) is in 17-26ms range. Mouse motions lag seems to be low too.
did not check all of the shots though. Counted only for 15.

Added G100s input lag test for mouse1
Added some thoughts on tolerance and number of measurements
Added CSGO with G100s
tested HPET enable/disable in win7
Removed OSU since the exact screen reaction time could not be determined on footage and it is useless for this game I beleive.
Added Q3A with G100s
Added non native DPIs for G100s
Added KB results
Updated G100s results with revised numbers.