Hi Zach --
Like MadRider I also live near the Tetuan metro. The whole Tetuan district is a very interesting area as it incorporates very upscale living with more middle to low income areas. It all depends on what side of Bravo Murillo you live.
That said I think the area is perfectly safe. Yes, there are many immigrants living in the neighborhood (myself included

) which can be seen as either positive or negative. I choose to see the positive... there is diversity.. not just latin american, but also Asian and African ethnic diveristy. With this diversity brings diversity in shopping options, especially food shopping if you are into cooking. Small shops specializing in Caribbean cuisine, Asian foods, African.. etc.
Many small internet caf�s (locutorios) and Bravo Murillo offers a plethora of shopping options as well as several movie theaters, including one on Reina Victoria (Cuatro Caminos) which offers films in original version.
I will say, however, that when I decide to dine out, I usually head for restuarants in the other neighborhoods such as Huertas/La Latina/Gran V�a/etc.