Looks like another TF2 Free weekend coming up and an extended one at that.  The TF2 Sniper Vs Spy update page has these tasty morsels and the amusing comic strip "The Insult"  It appears the April 1st Jarate update is in fact real.

Jarate

Jarate is a thrown jar that splashes upon impact. When splashed on enemies, they take 35% more damage for a period of time. Jumping in water will wash off Jarate. Jarate is also able to short out Spies’ cloaking devices. When used on teammates, Jarate will extinguish any fire effects.

* Jarate is neither affiliated with, nor a substitute for, Karate.

Just in case you missed it, the Day 6 Spy Unlock is The Ambassador.