Software Engineering is an interesting mix of practice and theory. On the theory side, you should make a habit of browsing / googling for things that are a good intersection of interesting to you and novel. Be forewarned, some of the common places to get information (like stackOverflow) can be very intimidating.
The standard expiration date for most checks is 180 days (six months) and personal checks are included in this policy. In the United States, banks are privately owned and not government operated so banks do have the right to refuse your deposit if there happens to be any suspicion of the item's negotiability.
The new Air Miles expiry policy can now expire; in fact starting December 31st, 2011, all Air Miles reward miles in your account will have a date stamp of 5 years. What this means is that any reward miles you have earned before December 31st, 2011 will have to be redeemed by December 31st, 2016.