I have tried it. Couldn't stand it. I hate having a different UI from the real website.
Personally, given the option between a desktop webpage, mobile optimized webpage or a native tablet app, I'd take the native app every day. (Especially when, like in the case of Tapatalk, you get *more* features compared to the webpage alone.)
Personally, I think most forum UIs are atrocious and stuck in the early-2000's, design wise. (Though some forums do have nice UIs; I'm particularly fond of the Something Awful Forum's User Control Panel; being able to follow threads, track replies, manage PMs, view unread posts, etc. all from a single page is *very* handy and one of the reasons I like Tapatalk, as it provides similar functionality).
I browse 4 or 5 forums regularly, using wildly different themes and forum engines. Having all those forums in one place, with a single UI makes it less jarring when switching between them.
Plus unified reply, activity and PM notifications makes keeping up with threads and users incredibly easy.
To each their own though. If the webpage works for you, more power to you!