Win7's built-in backup works fine as long as what you're restoring to isn't smaller than the original disk which is usually the case when you move from an HDD to an SSD. If you backed-up your 500GB HDD and only have 40GB of data, then try to restore to your 64GB SSD, it will complain about it.
That's just dumb, but I'm pretty sure it's just MS avoiding getting sued by other data backup software companies for ruining their market. The good news is you can get around it. I did once and it involved shrinking the partition. I forgot whether this took place before or after the backup. Shrinking it after involves mounting the VHD in Disk Manager.
By the way, the mountable read/write VHD it creates is THE 2nd BEST thing about the built-in image backup. If you just need to get one file, you can. If you want to add a file to your backup, you can. If you run MS's Virtual PC and want to boot off your VHD image backup, you absolutely can.