In case anybody else is also thinking of jumping to PlusNet (I am now in the process of doing so) ...
PlusNet's offer ends tomorrow (as MrSaffron told me earlier in the thread).
Topcashback's good offer ended yesterday.
Quido's good offer had gone before that, but one nearly as good is back (£117 for Unlimited Fibre Extra and £97 for Unlimited Fibre)
BT Infinity 2, thinking of moving to PlusNet