I didn't know who Seth Green was until I learned who's voicing Joker. I've never watched Buffy or Family Guy or anything. (I know, I'm missing a lot).
As was said before, I'd go for Joker even if he was voiced by someone else. Personally, I don't get the "fan-girling" over the VAs (as was executed in the Anders' thread). I like the characters because of their personalities that are usually diffrent from the personality of a VA. However, I understand that the voice is a huge part of personal charm, so I'd find it hard to admire Joker if he was voiced by, say, Gilbert Gottfried. XD
Don't get me wrong, I'm aware that voice-acting is important for it can completely ruin the character and I appreciate the great job the VAs are doing in BioWare's games. Plus, I know it's always nice to hear someone you've liked before the game (for me, it's Kate Mulgrew. You go, girl!) and that the particular VA is able to obtain new fans who are likely to support him in his/her other work.
I didn't want to rant about voice-acting, I was just disclaiming some strange freudian notion that every gamer subconsciously wants to romance the VA instead of the character.
And - Joker in German? It was interesting and strangely amusing, especially when he said Scheiße! Are there any other language versions? The thought of Joker speaking French is quite... intriguing