BioWare has already made it clear that importing your Mass Effect save files into Mass Effect 2 will have an impact on the storyline. What they didn't mention until now is that it affects the strength of your character, too.

"If you finished ME1 as a high level character you will receive greater bonuses than those who finished at lower levels," community manager Chris Priestly said on the BioWare forums. "Ex, if you finished ME1 as a level 35 character, you will receive a bonus, but if you finished ME1 as a level 50 character, your bonus will be larger."

"That being said these bonuses will not put new playthrough characters at a severe disadvantage. For example, some of these bonuses include a monetary boost at the start of the game, or additional research resources for use at the Normandy’s Tech Lab. Another perk is if you finished the game as a Paragon or Renegade, part of your alignment will carry over making it easier to access certain dialogue options."

Priestly also notes that you should keep your ME2 save files for when Mass Effect 3 rolls around.