Two weeks later and I have detected no problems when running Safari in 32-bit mode. As for me, I find the advantage of using it this way far outweights the benefit of running a 64-bit Safari. If anything, Safari seems faster-
A lot will depend on (a) how much memory you have in your computer and (b) how you use Safari.
The biggest advantage of 64-bit addressing is that it allows your compute to use more than 4 GB of RAM, the limit for 32-bit systems. If you don't have more than 4 GB of RAM installed in your system, then it'll make no difference.
If you *do* have more than 4 GB of RAM, then whether or not Safari will be any different depending on if it's run in 32-bit mode or 64-bit mode depends on how you use Safari. A program must be written for 64-bit addressing and running in 64-bit mode in order to use more than 4 GB of RAM itself; that is, if you install 8 GB of RAM but run 32-bit progams, those programs will only be able to use 4 GB of your 8 GB.
Is that a big limitation? If you only have a few windows in Safari open at once and you quit Safari when you're done, no.
If you use Safari like I do (I typically will leave it running for months at a time without quitting it, and at any given time I probably have 30 or 40 Web pages open in Safari), then it might. My Safari tends to slow to a crawl, because I only have 3 GB of RAM in my computer--if I were to install more RAM and run 64-bit Safari, my system would likely be significantly faster.