Your limit is a function of the resources you want your node to consume. Above that limit, your node either rejects large blocks that are spam (not accepted by the longest chain), or drops off the network because it can't keep up.
So does BU follow the longest chain or not?
If not, than it obviously can't work, as it was pointed out a million times already - everybody will fork off randomly according to their limit.
If it follows the longest chain, then your limit doesn't matter, as eventually you will have to switch (otherwise, again, you will be forked off).
Since BU can only work if it follows miners, your personal limit becomes irrelevant: if you insist on setting it, you will just hurt yourself and will still have to eventually switch if you plan to continue using Bitcoin.
This limit cannot be used as a signal to miners because of Sybil attacks, so it's pointless.
Yet BU proponents push it as the main feature of BU
It follows the longest chain as long as it can (based on your resources), and if it can no longer follow, it drops out.
The personal limit can be of value as a signal, since there is no automatism between your "vote" and increased block size.
There is little basis for the assumption that miners will be foolish enough to fall for a simple Sybil attack through this channel.
And BU proponents do not think this signal information is the main feature, that's a silly assumption to make.
My personal limit can mimic 2000 limits. Thus I can spoof the network to behave as if it is ready for 1.5MB. If the miners believe that, its only a matter of time.
We have covered this 10 times in the thread now, yet we are given no answer to how you would prevent an incremental Sybil attack like brg444 posted.