I am new to MikroTik hardware but think I'm on the right direction. Just started supporting more commercial businesses and they are using T1's and related business-class Internet connections for both their employee web browsing as well as phone connections. I would like to augment their rather slow Internet speeds with a simple consumer-grade connection (high bandwidth but less reliability). Could a RB2011 perform the load balancing to make this happen? Am I thinking correctly about this?

Yes it could. Depends on your needs.

For instance, I am supporting a building that has around 150 people. There is a VOIP PBX phone system, and plenty of Internet usage. There is a 6MB commercial Internet circuit connecting the building to the outside world right now so, as you can imagine, it is terribly inadequate for the job. We are going to be installing a 50MB fiber circuit to the site in the next few months but we need a solution to augment our connections NOW. I was pondering the idea of having some simple Cable-Internet service installed (which can also go up to 50MB but not symmetric or as reliable) just to tie into our connectivity "pool". I believe the phones are already on a separate circuit from the web connectivity so there isn't the need for QOS (just yet) but I haven't been able to see anything that mentions if a RB2011 does this particular task (or if there is a better networking solution).