How do I find the boot parameters used by the running kernel?

Is there a way to find out with what parameters did the kernel boot?

For example if I specify noexec=off at the grub command line? Can I see this sort of info after the system has finished booting?

You can run cat /proc/cmdline.

Example:

[01:31] ~ $ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-2.6.38-7-generic root=UUID=025c4231-b7bb-48bf-93e9-d20c5b5ce123 ro crashkernel=384M-2G:64M,2G-:128M quiet splash bootchart=disable acpi_enforce_resources=lax vga=792 vt.handoff=7