I just installed the FIND mod (RSS feeds, etc), and it would be beneficial to allow HTML. I know there is an HTML Admin Only mod, but I was wonder what the dangers are in just allowing it for the whole board? I really only need to allow a couple codes, like <p>,<br>,<b>,<i>,<u>, <a href...>, etc...
None really, but if you let <img> slip by you, then things could become a problem. Lately people have been using the <img> tag to use .php extention files for images. Sometimes these images are not images at all and are scripts which can carry malicious data and/or adware/spyware. Whereas phpBB has it built in to only accept certain file extentions for the [img] BBCodes such as .jpg, .gif, and .png and thats it. All others will appear as a broken link text. And good old <img> HTML tags carry no restrictions.
tags which could cause problems: <img>, <object>, <script>, <table>(allowing this can easily destroy your boards layout), I think you get the idea. If you really need a specific tag, I'd say add a bbcode for it. As well, when using bbcode, if you look at the pages source, the code outputted will be html, you wont see things like [whatever bbcode]text[/bbcode] in the source, so I dont think any RSS feeds should have a problem with it.