Re: ubuntu won't start after installation, raid 5
In the past when I've used software raid I've had to make sure that I have a /boot partition that's separate from the main raid array at raid level 1 which is of course mirroring so sda1, sdb1, sdc1 etc. are all the same. from there you can boot from any into any of these partitions and you will get grub. In hardware raid this wouldn't be necessary as the raid controller would deal with all of this but with software raid, the BIOS doesn't understand software raid partitions.
I now tend not to use software raid and instead favour lvm (Logical Volume Manager) which can be configured with parity like raid 5, the benefit of lvm is that not all of the members of the volume group need to be the same size so you can just have /boot on sda1 and have all the space on the other drives. This may suit your needs better so you may want to look into that.
Hope this helps!
Desktop: Z77X-UD5H, Intel i7 3770k, NVidia GeForce 660 Ti Sli 16GB DDR3 RAM 2TB HDD
OSes: Mint 14 x64 Windows 7 Ultimate x64
Laptop: Dell Latitude E6430
OSes: Ubuntu 13.04 x64, Backtrack 5 R3