Its about time he's been humiliated in public like that. The man seems to exist in a very Kim Jong Il style bubble surrounded by yes men and cronies determined to preserve the gravy train.
The whole process needs to be made to look like a circus, any shred of credibility needs to be destroyed in order to prevent Mugabe from selling himself as the legitimate head of state. Those MDC MPs need to sing, dance, heckle, abuse, yell, clap and stamp their feet as long as that Parliament is in session. They need to bring it home to Mbeki and Mugabe that they simply cannot sweep this latest farce under the carpet and continue on as before.
EDIT: it may not look like it, but as long as the MDC hold out and refuse to sign any deal on power sharing that betrays the people who voted MDC in the election, they have Mugabe and ZANU-PF by the balls. Mbeki will grow increasingly desperate as his reign as anointed President comes to an end and will in turn put more pressure on the two parties to compromise.