What is the recommended partition size for Windows 7 Home Premium?

Well, that depends. I'd recommend you allocate at least 20GB based on my experience with the RC. I'm currently dual-booting Build 7100 and Windows XP, which is why Windows 7 has its own partition.

But, if you already have you final copy and are planning to use it as your primary OS, there's no reason to use a separate partition.
 
If you just want to try it out, the previous post applies. If you are going to use the final release as your main OS, you would need at least double that amount of space or more. As you install more programs, get more updates and restore points, it will start to fill quickly.
My RC is currently using 54GB, Music, Video and photos are on a seperate drive, only applications and documents are on that partiton.
 
I recommand ether a small seperate drive, or a partition 60 Min -> 100 gigs. Not only do you need space for the operating system and for programs, You also DO NOT want to get below 16% of Free space. ie if everything would fill 50 Gigs, then the Partition should be no less than 60 gigs. Defrag requires some free space to shift files around And you have to allocate for hidden files.
 
Excellent points, all of them - but as a caution to the OP please be aware that you should not defragment an SSD - it's not necessary and all the extra writes can actually hurt rather than help performance.

(I don't know that he's actually planning to use an SSD - but what the hey, a warning couldn't hurt...)
 
If you have an SSD, Win 7 will detect it as such and 7's default behavior is to disable Defragmentation for that volume. If the installed SSD suports the TRIM command, then Win 7 will automatically apply same on an ongoing basis. Meaning, if you delete something from your SSD, then Win7 will run the TRIM command in the background by default and keep your drive running optimally.

This is different from Vista and XP - Defragmentation does not disable, and the TRIM command isn't natively supported for those OSs. You may download a tool to run TRIM on your SSD, but the OS won't do that on an ongoing basis. The User will have to manually run the tool from time to time. I should think that 3rd party disc utilities will (eventually?) implement Win 7's treatment of SSD's as their own defaults (i.e. detect and properly clean a compliant SSD with a TRIM command, but not run a defrag on it), but as of now I'm not aware of any available to the public.
 
I'm going to use a 64Gb SSD to run Win 7 Pro 64 and a 64Gb SSD for Adobe CS5 and scratch disk. With nothing else on each. If the sys SSD gets too full, I'll port My Documents to one of my 2Tb HDDs.
 
a partition is always 10 percent faster than the partition after it. So make it big enough for your applications you want the best performance of. If you want a partition for storage. Cut the drive in 2 or 40-60

Yeah but what if I'm using it just as system drive and nothing else. No programs, etc.
 
I've done half a dozen Win7 installs this week and the "base" install takes nearly 20GB in my experience. I'm writing post this on my new Win7 Ultimate rig, I've installed literally nothing but drivers and 20GB is used up already on my OS partition.
 
I tried to create 35g for 2 partitions of os/apps and backup. It was too small, and I ended using my backup partition for swap file space after it crashed. I am now rebuilding with 80 gig partition for OS/Swap/Applications. Applications and temp files take up space, as do restore points, and an 8 gig machine could use a 20g swap file by itself.

I never truely ran out of space on the drive, but it sure acted flaky everytime the space free got under 10g, and seem to be much more behaved after moving/deleting back to 10g free.

Just my 2 cents.
 
Minimum requirement is 16 GB for 32-bit and 20 GB for 64-bit as mentioned already but it is not the true minimum.

After a clean Windows 7 install (Ultimate, 32-bit), primary drive size is as follow..
Used: 7.78 GB
Free: 37.2 GB
Folders:
PrefLogs - 0 Bytes
Program Files - 391 MB (394 MB)
Users - 80.5 MB (81.2)
Windows - 7.32 GB (7.41 GB)

After you have installed your motherboard CD and done a windows update (important updates only), used size will go up to about 10 GB, install a few more of your favorite programs and it should swell up to 11-12 GB, with some 4 GB left off 16 GB..
So the true minimum for Win 7 is something like 12 GB.

So if you have up to 500 GB HDD, primary can be 40-45 GB (even 30-35 ish if you really want to do a scrooge)
For 1 TB and above, 100-150 GB straight up, you can afford it :)