XBMC streaming sloooooow

I recently tried XBMC on my Pi, and although I have a fairly fast (typically 10-20 Mb/s) internet connection, streaming video is abysmally slow - just a couple of frames/sec. I have read about other users implementing XBMC, and being seemingly satisfied - is this just a problem with my system, or is is peculiar to streaming video only? If YOU are watching streaming video using XBMC, can you give me some information as to how you have your system set up?
For what it is worth, I have the Raspbian Wheezy distro on another SD card, and Midori is also painfully slow, even with a fast internet connection.

What type of videos are you trying to stream? Are these 1080p rips with DTS sound etc?

Some stuff from PBS, initially. XBMC is so slow in general on the Pi that it is difficult to work with. Mouse tracking lags substantially, almost all of the video add-ons I try to access report no media in them, etc. I am just so surprised after seeing demos of other graphics apps (like Quake) and XBMC running nice, fast video.

I had the same problems in XBMC (slow network access, jumpy mouse) until I changed from an 800mA wall wart to a 1A. At least I think that's what solved it for me ...

[dom]

For what it is worth, I have the Raspbian Wheezy distro on another SD card, and Midori is also painfully slow, even with a fast internet connection.

Check dmesg log for errors. You may have an incompatible USB device (like a keyboard that requires too much current) plugged in, or your power supply may be dropping too low when loaded.
If you are able to swap power supply, power supply USB cable, and USB devices you may be able to identify if one of those is causing the problem.

I've tried Raspbmc streaming YouTube HD videos (via the YouTube addon) and it works with no lag what so ever.
I agree the GUI is a bit slow at times but the HD YouTube videos play fine.

@mrfish

is your xbmc still running well? because mine shows exact the same problems (slow, mouse laggy). can you give other tips to get it running faster?

I feel really stupid, but I realize that I should have said I'm running Raspbmc, NOT XBMC, in case anyone was confused. The difference may be minor, but I wanted to clarify.
At any rate, I have been out of town for a while, so no updates on streaming video, but I did load some mp4 files to a flash drive & they seem to play OK in Raspbmc. If I could get the streaming working acceptably (and especially if I could get Realplay working) this would be a sweet setup.