Will report back once it's done.
Bummer, midway through downloading the blockchain, with -dbcache=2000, it kept using up RAM all the way to 4GB and then crashed.
On restart, it sits at the wallet picture with "xporting blocks from block databas" (text cut off on left and right hand side). I can see from the Task Manager that it's doing something, pegged CPU at 50%, and increasing RAM. I'll let it sit and see where it goes.
Edit: It finally came out of the splash screen and CPU usage dropped to normal, but RAM is still increasing. I've got it set to -dbcache=1000 this time, so we'll see if it sticks to that.
I closed the instance running -dbcache=1000 to see how it would handle it, and it closed no problem. I've restarted it with -dbcache=1500, and have let it run for a while. Memory use is now up to 1,660,316 KB, so, similar to my results using -dbcache=2000 where it went up to 4GB, it doesn't seem to be minding the value chosen in this setting as a limit.
I see similar issues with memory usage. I built bitcoin-qt v0.8.0rc1 on Windows and tested it by downloading blocks from scratch, clearing the data directory each time.
On the first attempt, I ran with "dbcache=1000" and "txindex=1" in bitcoin.conf (though I'm not sure the txindex setting had any effect, because I saw "LoadBlockIndex(): transaction index disabled" in debug.log). It eventually crashed, and there were many bad_alloc exceptions in debug.log.
On the second attempt, I did not use any special options. Memory usage gradually increased to 2200MB while downloading blocks, and then decreased to 1650MB once downloading was finished. Perhaps the decrease was a result of freeing the blocks stored in mapOrphanBlocks, which I believe contained several thousand blocks that had been downloaded in reverse.
It seems there is a memory leak during initial block download. If this will affect all new users, it seems rather important to fix.
I'd run it from scratch again myself without any special options, but something about having all the connections from Bitcoin over time causes the router I share with others to slow to a halt, and I don't have access to it at the moment to reset it when this happens.
Which version of Windows are you using?