Attention to things like grammar and spelling are a crucial part to having a successful blog. By its very nature, a blog is going to be less formal than, say, a magazine or newspaper. The blog author is totally free to change point of view or type of content offered.
But do put effort into making sure that each piece you write looks professional. Havi g thgs lk dis may look gr8t in a txt but are annoying in a blog post. Don't use text abbreviations or tons of slang. Make a point to go back and read through every post to check for spelling errors.
If you want people to take your blog content seriously, you must show that you care about your work. Remember that your most popular posts are not always going to be the most recent ones. Often times it will be the posts that have been around for awhile and have had time to filter into the internet.