Lenovo promised that it would begin offering an Android 4.0 in May and true to form, the update is rolling out now in some regions. In a comment on Lenovo's forums, a representative said that the UK and WE versions of the update should be arriving over-the-air now, with US certification slated for June 8th and the rest of the world waiting for a month after that. Some members in the forum have reported receiving the update already and are reporting good things, including functioning GPS, faster speeds, and the all-important compatibility with Chrome Beta for Android. If you're a ThinkPad Tablet owner in the UK or western europe, the OTA update to Ice Cream Sandwich should be available now.
Thanks, Patlex!