vlevi: The biggest reason for a 64-bit PL/SQL Developer is so that it is compatible with the 64-bit Oracle client. PL/SQL Developer rarely breaks the 2GB memory barrier (you know 32-bit apps can only access 2GB of addressing space, correct? And that fragmented memory can cause applications to throw out-of-memory exceptions long before they've used all of this?), however it has happened on occasion. In fact, there are a lot of operations PL/SQL Developer doesn't handle very well, including a large set of inserts, and copying the results grid with large resultsets.
As for "a 32-bit app cannot kill the whole machine", your problem isn't your memory; it's most likely your swap file settings, your hard drive, fragmentation on either of those, or a very slow PC. No single application can kill the whole machine easily; the whole point of the Windows OS is to isolate application issues, and you have to have a lot wrong to take your PC down from one application hogging memory.
Each app has a memory priority, just like its process priority, and though you can't see it in task manager, the OS trumps both by having the highest process and memory priority. The only way you can take down the OS is if the OS itself (despite being top priority) can't keep up with the actions you're asking it to take (such as paging memory). Most likely your swap file is set to automatically grow, you have a physical hard drive (not SSD), and your drive and paging file are fragmented as h***.
Also, Firefox cannot allocate 3GB of memory unless you are booting with a special 3GB memory switch (or have executed an editbin /largeaddressaware against the fx executable), and if that's the case, I think you are messing with things you may not fully understand. It's true that 8GB is just a higher limit that could be hit by running fx as 64-bit, but throttling the individual processes' memory usage to keep them far below the machine's memory isn't the way to resolve issues like this.
Regardless, I would prefer to have everything be native 64-bit. As with the 16-bit -> 32-bit conversion back in the days of Windows 95, running 32-bit apps on a 64-bit machine takes a performance hit. It may not be noticeable on a good machine, but apps that run natively in the OS's memory space are always preferable. I doubt you wish apps were still 16-bit... moving to native 64-bit is the natural progression of processor capabilities, and applications need to keep up with the times.
