In the past several hours there have been at least two blocks with a sufficient number of transactions per block to leave bitcoin nodes relying on Berkeley Database for block handling to wedge when set to the post March 2013 limit of 40,000 database locks and objects. For a few hours doubling that amount to 80,000 sufficed until a still more complex block arrived. A patch has recently been published which should remedy this issue until such a time the universe undergoes heat death. The patch works by raising the maximums Berkeley Database is configured with in order to handle any number of transactions that can fit into a Bitcoin block. On some platforms like OpenBSD which aggressively allocate memory in advance for safety reasons Bitcoin's RAM usage is increased noticeably with this patch. If your system enforces low per-process memory limits you may have to edit you system's settings.