If you're not upgrading until summer, you may be asking your question a tad early. Most recommends now would tell you to wait because of driver and application issues, as you mentioned. That situation may change by the time you get around to it.
Still, if you’re concerned about it, I'd venture to say that even by the time you do get to it, you'll want to stay with 32-bit Vista unless you’re dual-booting with XP and all your apps are working there. That would take most of the sting out of your upgrade if you do decide to future-proof your PC with 64-bit Vista. But let me emphasize again, if you’re not dual-booting, don’t bother until you have a good reason.
i highly recommend 32 bit. and this is coming from a dude with 64 bit...
applications aren't the issue (Vista 64 bit can run 32bit applications on the the fly). it's the driver support for 64 bit vista that's atrocious.
right now I'm using BETA 64 bit drivers for WinXp to get my Linksys 802.11g card to work. and what a pain in the ass it was... i still don't have 64 bit drivers for my RAID. i have an entire 200GB hard drive with info on it that i can't access.