Mass-effect – Victus and Wrex have disappeared

• Kasumi, Jacob, Miranda, Zaeed, Jack, Grunt, and Samara can all be recruited as war assets if they survived ME2 and events in ME3.

• The strength of the Normandy is effected by the amount of upgrades applied in ME2

• Having a lot of mineral resources at the end of ME2 may grant you a bonus of up to 100 war assets.

• The Destiny Ascension can be added as a war asset provided it survived ME1. This reduces the strength of all of the Alliance fleets.

• If the Destiny Ascension was destroyed, the strength of the Alliance fleets are boosted, and a new Alliance Admiral is available.

• Zhu's hope colonist are a war asset if they survived ME1.

• The Rachni can be recruited as assets if you allowed the queen to live in ME1.

• Conrad Verner can even provide a war asset provided you did a bunch of random completionist quests in ME1

• Wrex and Mordin surviving ME 1 and 2 and what Mordin did with the genophage data have a big effect on the amount of war assets that can be generated from the Korgan.

• If you did not complete Arrival, the a Alliance 103rd marine division is weakened.

• Captain Kirrahe can bring in elements of the STG provided he survived Virmire.

• If you completed Bring Down the Sky and the Batarian leader escaped, he can be recruited to strengthen what's left of their fleet.

• The Archer bothers are available as assets if they survived Overlord.

• Destroying/not destroying the Collector Base effects the value of an asset found in the Cerberus base.

• If Kelly Chambers survives ME2 she can help recruit some ex-Cerberus engineers.

• Reprogramming the Geth Heretics increases the strength of their fleet if you can recruit them, but weakens the Quarians.

Every Mass Effect 2 save file has a "QuestCompletion" variable that can be one of three values. Gibbed's save editor has dubbed these, "Quest Incomplete", "Lived To Fight Again", and "Went Out in a Blaze of Glory".

There is no "mission complete" save generated by ME2 like there is in ME1. Instead, every save file has this variable in one of the three states. Presumably, only saves where Shepard "Lived to Fight Again" will be viable to import, as Bioware has previously stated dead Commander Shephards won't be importable into ME3. (And obviously, you can't import without beating the game).

(Related: https://gaming.stackexchange.com/a/52493/336)

When importing into Mass Effect 3, you get to pick the actual save to import (i.e., quick, auto, or manual). Your save is always current, so there should be no worry about keeping your save "updated", other than simply saving normally from playing the game.