I like my ThinkPad and I appreciate the flexibility I get from managing network connectivity using ThinkVantage Access Connections. However, the ThinkPad got into a state where any change to a wired or WAN Miniport profile caused the Ethernet connection to fail with error "DHCP server not responding." Wireless connectivity continued to work, although it took me a long time to figure that out.
Similarly, any change to the Access Connections (like trying to upgrade to the current version) caused wired connectivity to fail.
For a long while, the only solution I found was to revert changes using Windows system restore. Last weekend I decided I had had enough, and spent the time to out-stubborn the problem.
It turns out that deleting and re-adding the Ethernet NIC using Windows Device Manager and Add New Hardware did the trick. I could now change profiles, upgrade software, etc. without breaking my wired connection. Good!
However, deleting and re-adding the NIC broke all my WAN Miniport connections. VPN access and even dial-up no longer worked. Happily for me, "harrisb" had posted a solution for this one on a Lenovo forum: http://forums.lenovo.com/lnv/board/message?board.id=Special_Interest_Windows&thread.id=398 It's one I would never have figured out on my own!
So, I am back to being a happy ThinkPad camper.