I understand litangel's concern about "knowing how the players will play during 2010," since that will take us away from trying to guess the future, like in real life, where a manager's baseball knowledge and scouting expertise will give him/her an advantage.
On the other hand, that is always the case during a second season with the same card set. This is already a simulation, though, so maybe it's not an issue, after all. We would all have the same knowledge base, so that would just become one more element of the game.
I do agree with Rant that two seasons with fixed start dates would be best. From scanning the forums, it looks like most keeper leagues draft in late March or early April, right after the new cards come out, and then once again in July or August.
If we want to avoid competing for managers' attention in those time frames, then we still need to find later times in the year -- and with memorable start dates. For example, perhaps we could routinely start the draft on the day after Memorial Day and then the day after Thanksgiving.
Or if conflict with year-end holidays would be an issue, then maybe draft on the 5th of July and the 5th of January?