By long-term, I don't mean where your gonna find fresh content for next months update ... I'm talking like ten years down the road. Here's my two cents:

(1) Legal: while there is no enforcement of obscenity laws for Internet users right now, don't think that it will always be this way. Sure, you can make a quick buck by running a bunch of free sites today, but you might not be able to do so in ten years. That's why I highly recommend setting up a site using something like an age validation services or similar techniques. That way, you won't be scrambling to add an AVS to all your sites. Your sign-up page will already be tweaked, and you will be able to make such a change with minimal disruption in services. Stay ahead of the game!

(2) Diversity: don't put all your eggs in one basket! If you have a members area, don't use just one content provider, use a couple of different ones. Wouldn't it suck if you used content provider "X" exclusively for all your sites, and then suddenly they shut down? Damn, you'd be out of business too!

This goes for every aspect of your business: setting up a second site? Try not to use the same host; if their servers go down the all your sites would go down at the same time. Have an Adult Check site? If a surfer don't sign-up, send them to your Age Check site using a console. Perhaps they already have a Age Check ID and you can make something from an upsale.

(3) EMail Lists: if your not collecting email lists, your missing the boat! Give surfers some method to contact you on your sites; and everytime they do, save their email address somewhere. Over the years, these lists will grow and could become a massive revenue source for you! IMHO, email is the absolute best traffic... a surfer has your undivided attention when reading an email; you are the only site listed, unlike a search engine with a million other sites listed.

(4) Taxes: Most sponsors seem to pay with a 1099. Don't be surprised come April that you have a massive tax bill waiting for you! If you are making good money, perhaps you should consider making quarterly payments to offset your tax payment. Some sponsors are overseas, and don't share information with the IRS, but this does not mean you don't hafta pay taxes on it! You are still be required by law to pay taxes on any monies earned overseas.

(5) Automation: Using CGI scripts to automate tasks is a great way to create a self-sustaining web site! Things such as a picture of the day or a link exchange are great ways to bring traffic in to your site, and using automation takes all the work out of those tasks! By creating an automated website, you can be making money years down the road without ever logging into your FTP!