Recently i have installed Windows 7 in both of my laptops. In my personal notebook (Sony VAIO VGN-FS315M) i have installed 32-bit version of Windows 7 as it has a 32 bit processor. The other laptop from work (DELL LATITUDE D630) has got a 64 bit processor, hence i could install Windows 7 64 bit.

32 bit and 64 bit Versions of Windows refer to the way a computer processor handles the information and its natural that 64-bit version of Windows can handle large amounts of random access memory.

Now why did you i switch to 64-bit version, well why not. According to Microsoft if you have more than 4 GB RAM installed, the switching is apparent and i acknowledge that. I am not a Microsoft fan nor am i advertising/promoting them. But we are Windows users anyway. Microsoft already did a lot of advertisement for Windows 7 (lot of testing has been done, better user friendliness and blah blah) defending the criticism for Windows Vista. 

Installing the Windows 7 is pretty straightforward but after switching, one of the challenges is to find the drivers for the new OS. I really had hard time finding drivers for VAIO VGN-FS315M. This series is discontinued and there is no support from Sony. Old drivers are for Windows XP. One tip, find the drivers for VISTA(32 bit). DELL D630 found all the drivers by default. Most important challenge for Windows 7 is finding the 64-bit versions of the software you need. Many of them are not stable yet, for example Firefox has  currently a pre release (64-bit) version. Adobe flash player doesn't support 64-bit browser yet.

At the end of the day it will be your decision whether you will switching to Window 7 or not. Just remember that you are going to face the above mentioned challenges and don't forget to make a backup of your Data before switching to the new OS (in case if anything goes wrong).