The problem with marketing your services blindly on forums like these is that you'll only be visible to the people who are here looking for a bargin in the first place. If they see your company offering 5 GB of space for 5 bucks per month and then they see Joe Blow's Kiddie Hosting Emporium offering 50 GB of space for 5 bucks per month, who will they go for? Clearly the guy offering 50 GB of space is overselling his server(s) because there is no way that if everybody on his machines uploaded 50 GB of data that the servers would sustain themselves. But remember, your average customer is not going to realize that. They see bigger numbers for the same (or lesser) value and jump all over it.
These days, you CAN'T compete because (as mentioned above) the market is too saturated. It's not like it was 10 years ago. Your average customer is not as wise when it comes to shopping around in regards to reviewing the background of the business they choose to go with. It doesn't matter to them. If they choose a fly-by-night to upload their worthless forum to, and the host disappears a week later, they'll just move somewhere else and think nothing of it.
In my experiences, if you really want to do this right, you need to establish a location locally in your town, not just online. Market your services to the local businesses around town. Send out literature in the mail, advertise in the local paper. Meet with people face to face. Take phone calls. Answer questions. Offer to help them transfer to your server. Explain to them why you're the company they can trust with their info. Explain why your services are worth the price that you're asking for. Locally based customers are more loyal and they are more likely to appreciate the fringe benefits of having a face behind your business name and a voice they can talk to when there's a problem/question. They're also more likely to appreciate features like no oversell policies, uptime guarantees, etc. In addition to that, they're not gonna just fill your server with warez, bot scripts, and junk.