As far as free webhosting goes, it largely depends who you get it from. Most don't allow the .htaccess files, that come with the SMF installation package, to be uploaded, which means you can't run an SMF based forum from them (at least not with any degree of flexibility or control), and the bandwidth/storage limits usually mean your database can't be overly large, either.
Then there's the ads... and they are majorly annoying. I've only found one halfway decent provider that will allow the file upload and doesn't (as far as I know) put any ads on your site.