Rob Bradshaw has posted an on-line version of an interesting article by F.F. Bruce:
F.F. Bruce, "Textual Problems in the Epistle to the Hebrews" in David Alan Black, ed., Scribes and Scripture: New Testament Essays in Honour of J Harold Greenlee. Winona Lake, IN: Eisenbrauns, 1992. pp.27-39.
He discusses the following passages: 2.9; 3.6; 4.2; 6.2; 9.11, 19; 10.1, 38; 11.11, 37; 12.1, 3.
He has a view of 2.9 I hadn't heard before: that neither variant was original!