+ sure it's better to do download a font and then use it over a graphic substitution in many places on a site
- but is it worth it to download it just for one title ? for one logo ?
That's EXACTLY the decision a good designer has to make. On my art studio's site I use graphics-as-text for almost everything except body text. Few people visit more than two or three pages (it's a tiny site whose audience is mainly people who know us in person), so the filesize of an embedded font would be more than the filesizes of the separate image files. And given the nature of the site, I really don't think I have to worry about visitors with images turned off-- though the alt and title attributes are duly populated all the same.
Conversely, one directory of my personal site uses an embedded font for the headers. There are tons of pages so I would never have taken the time to make all those image files-- but each page includes a big jpg that's already bigger than the font. Or, at least, bigger than one of the two font files. w3 is silent about whether UAs should download all forms in a batch, or wait and see whether a particular page actually requires italic along with plain.
My embedded fonts are essentially crippleware. Make a copy in a font editor which, ahem, I paid for
and delete everything that can never occur in a header. That means at least half of the Latin-1 range (I keep lower-case letters just in case, but dump capitals), everything in higher ranges except curly quotes and similar essential punctuation, and even some ASCII. (How often do you use angle brackets <> in a header? carets? ASCII tilde? backslash?)
I do this mainly so the download is kept to a reasonable size. But it also means that the user can't grab the font and use it for their own purposes, because there are too many missing pieces.