Slow to change between profiles

Hi All

I wonder if anyone can offer an explanation as to why my macbook pro has started to take ages to swop from on profile to another? It seems to close the active profile reasonably quickly, but once you select the alternative profile, it takes some minutes to boot up. The machine seems to be working well other than this, although I do feel like I have seen the rainbow wheel a lot when the machine is performing certain tasks. I would say most noticeably when opening a new application.

If anyone can help me with a possible cause or solution I would be very much obliged. Is there a chance that upgrading the OS to Mountain Lion might resolve this?

Many thanks in advance for any help you can give my.

Ron