I have blogged since my first year of vet school, and really like having a record of what I was learning and feeling about school when I started versus today. It's been helpful in connecting with fellow students and pre-vets, and it's fun to occasionally get linked to by other vet students or animal-related blogs.
That said, you do have to be careful. I write under my real name and write as though fellow students and future employers will be reading it. Some people use a pseudonym and then have more freedom to talk about classes and patients and things, but I feel like with so few vet schools, someone will eventually figure out who you are.
So, I say go for it! I blog with Blogger, because I really dislike the SDN blog format. I think the most extensive list of vet student blogs I've seen is on
http://allbutonespecies.blogspot.com/ .
Enjoy!