Hola AliMac!
Personally, I am all about adding your brand to the end of your title tag if your brand is not already associated with your product/services. However, if you are already ranking well for your brand i.e. You show up first for branded searches like Pepsi .com showing up when Pepsi Cola is searched, then I don't think it's necessary to have your brand in all of the titles on each page. Just include it in your about page or something to that effect.
With regards to abbreviating your business's name, Unless your business is commonly referred to as the abbreviated version of your name, I wouldn't include it in the Title. Also, if you have a long business name, I think it's more enticing to write a compelling title that includes keywords than it is to include your brand name.
How does this affect SEO? It really doesn't. There is no bias for branded titles. See this blog post by Rand on Search Engine Land.
I hope this helps!
B/R
Will