The result is that 0.7 (by default, it can be tweaked manually) will not accept "too large" blocks (we don't yet know what exactly causes it, but it is very likely caused by many transactions in the block).
The "manual tweak" is exactly two lines. Anyone can apply it, because the recompilation is not necessary. All it takes is to create a short text file and restart the bitcoin client.
https://bitcointalk.org/index.php?topic=152208.0Block size isn't the problem, it's the BDB.
The limitation is not related to block size, but rather number of transactions accessed/updated by a block.
In general, the default for 0.8 (250k) is fine. Raising that to 500k is likely just as fine.
But it is not very simple to answer the question, because this 0.7 BDB lock issue becomes more complicated with larger BDB transactions.