http://chartbeat.com and http://haveamint.com are great for real-time analytics. I'd recommend them to anyone who:
1) experiences spikes in traffic and needs to adapt any load-bearing or server settings, etc. on-the-fly;
2) and/or is looking to figure out where random, but brief bursts of traffic are coming from, e.g. a foodie blogger who gets a bunch of traffic from a big food site news article and wants to jump in on the conversation mentioning them as it happens;
3) and/or has cat-like behavior and could just sit and watch meters all day.
EDIT: Also, for heat-mapping/usability testing: http://clicktale.com is good (though somewhat unreliable in my experience) and is probably the most cost-effective solution you'll find for SMB. I've never used http://userfly.com but it looks decent and seems to have gotten good reviews.