Are there any drawbacks of "/3Gb" switch in boot.ini for 32bit Windows?

On a desktop machine, there are likely no problems. The kernel paged pool is smaller on a W2K3 / WXP machine w/ the /3GB switch set. This is probably not an issue for a desktop machine because you shouldn't be coming close to exhausting your kernel paged pool. On a server, exhausting the kernel paged pool will cause you problems, and it's much more likely you could exhaust it.

Here's some good detail about the kernel memory considerations associated with the /3GB switch. If you really want to, you can fire up the NT kernel debugger and profile your system before and after the change w/ the information in this doc: http://blogs.technet.com/markrussinovich/archive/2009/03/26/3211216.aspx

You will have less memory available to your kernel - the switch adjusts the kernel mode address space/user mode address space split, previously 2GB to 2GB, to 1GB to 3GB. Read Raymond Chen's post on /3GB, and the follow-ups, before proceeding.

Before making any changes, you should first check if the processes you want to run are linked with the LARGEADDRESSAWARE flag. With the flag, there will be no changes to how the process uses memory.

You can use the SDK Tools for this:

dumpbin /headers exeName

The headers spit out should include:

Application can handle large (>2GB) addresses

I did the check on devenv.exe and in VS2008 it does include the flag.