i'm not sure who would be crazy enough to accept a check from a stranger for that amount...
I cannot think of any reasonable reason to not use cash in this type of transaction.
I happened to be boarding a plane early afternoon, but only having the fully-cleared funds, sufficient for all the BTC I wanted to buy, in my checking account at the end of the business day.
So, anyone depositing such a check into their own account would have had it clear at the end of day, same as any other good check. But, I couldn't have the full $3K cash-in-hand for a local transaction before boarding my flight.
Since some in the bitcoin community seem to care about 'tainted' coins from events like the Linode heists, it also benefits me to be able to make a check out to a person that I also get to know in real life. If the BTC they give me then has a strong taint, I can at least point out where it came from.
As it turned out, I used BitInstant. Their single-transaction maximum amount was enough for the time being, less than I wanted but a total that I was able to counter-deposit in cash. Worked well though the effective fees were quite high. Stupid 'Golden Week'.