I'm planning to install a SSD soon, and I want to make sure I get all the boot time benefits. Right now, I have Windows and Ubuntu installed on two separate HDDs. The Windows drive contains the MBR. However, I'm planning to replace the Ubuntu drive with the SSD. Will relocating the MBR to the new SSD have a meaningful effect on my boot time?
MBRs are very small (512B or more), so you won't get any increase from that.
However, there's also the spin-up time to consider, so depending on the HDD, can take up to about 30s by, for example, Hitachi's OEM specifications.
SSDs, not having moving parts, don't need to spin-up, but they still take time to go from standby to reading.
Really, unless you're rebooting very frequently(more than once a day), you won't notice a difference between booting HDD and SSD normally.
If you reinstall your operating system, put the boot record on the SSD. Otherwise, just leave it on the HDD. The effect will be minimal.