I just finished a novel that was written partially in first person, present tense. That struck me as unusual in the beginning, but once I got into the meat of the story it was not at all cumbersome or bothersome. In fact, it really just faded into the background and seemed entirely appropriate a stylistic choice once I finished the book -- the protagonist was a 15-year-old boy and there were duel narratives (the other in plain old third person, past tense). So I'm going to side with it being perfectly valid, but the skill of the writer needs to make it work.