Options from lesser to greater learning curve:
(1) menu > settings > applications > manage applications > [unwanted app such as weibo], then
force close +
uninstall(2) and if that doesn't work, then
root, and then try (1) again. (For info, consider
Rooting for Dummies)
(3) or if still unhappy and now that you've rooted, consider flashing a custom rom (aka replacing the android operating system you have now with a different one downloaded from the internet).
There are
many different roms, all with their own quirks and highlights. Do note that if you are using a bought, unaltered Samsung Galaxy S II, then some of the features you see now are NOT Android, but are instead Android + Samsung UI (+ some China specific mods).
ROM options:
back to basics, pure android, no samsung ui, no China mods:
flash a stock rom.
back to mostly basics:
cyanogen, a popular, mostly stock rom.
back to samsung:
flash original firmware (which will also de-root your device.)
or, go wild:
available romsThere's probably more links out there too.
As for the market, yeah, as far as I know, access to the Android market is restricted in China. I don't use it much so I don't know. But in regard to that, and assorted other sites of ill-repute, Various Purple Nightdresses work on smartphones.
All of this I learned from screwing around with my HTC Desire (and Google). YMMV.