I must say, I do find the tendency to deliberately spell incorrectly, use those indolent shortenings ("i h8 ur terramasssalater", etc.) and intentionally atrocious grammar to be one of the most hideous manifestations to sprout from the fervent loins of the internet and portable text communications devices.
I would, on the other hand, add that internet fora are a somewhat informal venue for discussion, and as such close attention to one's grammar is should not be fundamental in the minds of those utilising such; a certain amount of adherence to the conventions of grammar and spelling is, however, necessary if one is to convey ones point in a coherent manner. As such, I do not think that one should get agitated by accidental typographic errors, poor apostrophe use, errors based on homophones, and even malapropisms within such a setting, unless such actually becomes unreadable or otherwise incoherent - and I have made such mistakes on several occaisions in the past. In addition, I feel it apposite to add that some aspects of grammar and spelling can be rather contentious, and attempts to regulate such only lead to debates over such irrelevancies as the Oxford comma, the split infinitive, et hoc genus omne.
Of course, I am probably not the best person to comment on this phenomenon, as I suffer from what could be construed as the opposite problem. To whit, my postings have a tendency to read like a Victorian Military Manual.