If you are considering whether to buy a 32 or 64 bit system, then buy a 64 bit system.
Buying a 32 bit system now would be like buying a 16 bit system after 32 bit came out as the standard.
64 bit is the standard now, almost every new off the shelf computer is 64 bit.
Some day they will start coming out with 128 bit computers, then we'll go through this all over again.
As others have pointed out the main thing is ram, I don't think you can get many new computers with less then 4 and many come with 8, you have to have 64 bit for that.
My friend just got a new computer like mine but 2 years newer, and his computer has 16 gigabytes of ram, by the time I get a new computer it will probably be 32 or 64 gigabytes of ram.
I run a lot of 32 bit programs on my 64 bit computer and everything runs a lot faster then it ever did on my old computer.
Even if there is some penalty to running 32 software the other factors in a new computer make it so much faster then whatever you are running on now you won't notice the difference, but you will notice the difference if you run 64 bit software on a 32 bit computer.
Even if you don't need it now you will in the future.
And ram is really cheap now get as much as you can.
My first computer had 4 megabytes of ram, and 100 megabyte hard drive and a 25 mhz processor.
Now I have 8,000 megabytes, if ram and and 2,000,000 megabytes of hard drive space, not counting external drives and 4, 3 ghz processors.