This brings us nicely on to the subject of:

Why can we not play as female infected?

Female boomer would be hawt.
And just imagine the things a female smoker could do.

Update: < realises that he has just gone from pro-female to sexist very quickly >

L4D Update
A required update for Left 4 Dead has been released. Please run hldsupdatetool to receive the update. The specific changes include:

General
- Fixed Survivors being able to climb surfaces marked for versus infected only.
- Fixed a class of SurvivorBot bugs dealing with rescuing downed players.
- Players can no longer grab ladders while flying through the air after a Tank punch.
- Shooting near a car with an alarm that has already fired the alarm will no longer make chirping noises.
- Improved loading time.
- Fixed mini-gun physics exploit.
- Fixed propane tanks (and other physics objects) causing players to fall through elevators.
- Fixed rare achievement bug issues.
- Fixed several map exploits.
- Fixed various match making issues.
- Fixed NAT traversal issues.

Versus Changes
- Added HUD elements to show status of other infected players.
- Changed color of infected player name in chat to red.
- Fixed exploit where players could spawn infected bots
- Fixed instance where a Survivor changing to the infected team would be attacked by infected bots.
- Normalized special infected melee damage.
- Made the following client commands cheat protected: "Kill" and "explode".
- Fixed exploit where infected players could run away and teleport back to gain health.
- Players can only change teams once per map.
- Players can't change teams while other players are still loading.
- Tank spawns at the same % through the map for both teams in versus mode.
- Made the Tank and Witch spawn directly on the escape route.
- Increased chance of getting the Tank or Witch.
- Fixed team swap issue.

Hunter
- Easier to pounce a Survivor who is meleeing.
- Increased Minimum damage a Hunter pounce does.

Smoker
- Fixed Smoker tongue tolerance.
- Smoker now has to be killed or the tongue destroyed for the tongue to break.
- Survivor's cannot bash someone off the tongue until the Survivor being pulled is paralyzed or hanging
- Tongue attacks that fail to paralyze or hang a Survivor will use the shorter ability delay timer.
- Fixed cases where the ability timer was not using the correct time.
- Fixed case where you could point at a Survivor but not register a tongue hit
- Fixed Smoker tongue not targeting and landing properly through PZ ghosts.
- Smoker tongue does damage every second while dragging paralyzed Survivors.

Tank
- Bashable objects now appear with a red glow.
- Tanks hitting a car with an alarm disables the alarm permanently.
- Tank frustration timer is only reset by hitting Survivors with rocks or fists.
- Reduced autoshotgun damage against Tanks.

Witch
- Witch spawns at the same % through the map for both teams.
- Avoids spawning within a certain % of the tank.
- Fixed an exploit where the Witch could be woken up and tricked into attacking Survivors.