I posted a few weeks ago via my Sony E-Reader and I find it klunky as well.
You have a slight advantage in that you have a keyboard (I assume you have a Kindle w/a keyboard). The Sony has an on-screen keyboard operated either by fingers or by the stylus. Browsing the Web on the Sony is generally not fun (too much work) and posting to any site is just not worth the time. If I'm using the e-reader I think I'll just stay off the Web (besides, when I go on-line with the device, battery use is much diminished).