Just put up a new 10m antenna: a converted "Station Master" 27MHz CB antenna. It's just an end fed half wave aluminium pole with a homebrew matching unit.
The matching unit is just a 13 turn autotransformer wound on some 15mm PCV pipe and tapped at turn 4 (ish). The parallel tuning capacitor is ~15cm of RG58.
The first WSPR Tx gave a lot of spots:
2011-11-09 00:30 VK2MEV 28.126030 -25 0 QF57ua 10 N6GN CM88ok 11861 55
2011-11-09 00:30 VK2MEV 28.126048 -25 0 QF57ua 10 WA7HL DM51ck 12558 66
2011-11-09 00:30 VK2MEV 28.126024 -21 0 QF57ua 10 KF7O DN06tb 12568 49
2011-11-09 00:30 VK2MEV 28.126052 -22 0 QF57ua 10 ZL1JA RE66ir 2155 128
2011-11-09 00:30 VK2MEV 28.126041 -19 0 QF57ua 10 VK2XN/2 QF59ar 340 332
2011-11-09 00:30 VK2MEV 28.126052 -4 0 QF57ua 10 N7GLS CN85qo 12249 48
2011-11-09 00:30 VK2MEV 28.126030 -18 0 QF57ua 10 K6PZB CM88nk 11855 55
2011-11-09 00:30 VK2MEV 28.126044 -18 0 QF57ua 10 W5CGC EM13ka 13722 70
2011-11-09 00:30 VK2MEV 28.126030 -24 0 QF57ua 10 VE6OG DO33 13220 43
2011-11-09 00:30 VK2MEV 28.126009 -18 0 QF57ua 10 KO6SY DM14ka 12074 61
2011-11-09 00:30 VK2MEV 28.126014 -22 0 QF57ua 10 W1MNK EL87uv 14863 81
2011-11-09 00:30 VK2MEV 28.126044 -9 0 QF57ua 10 N7KJW DM43au 12492 63
2011-11-09 00:30 VK2MEV 28.126020 -18 0 QF57ua 10 VK4ZBV QG62ml 620 12
2011-11-09 00:30 VK2MEV 28.126041 -4 0 QF57ua 10 AC0NM DM12jt 12004 62
No complaints there! Those -4dB spots to the US are very encouraging :).
Attached is the current version of my AVR WSPR audio source code. It's written and tested on an ATMEGA8L running at 4MHz but thanks to AVR's fairly general architecture it should compile and work on a large number of AVRs.