I don't have any statistics for you but have a marketing idea for you if you plan on marketing your townhouse yourself....
You can create a flyer on Postlets.com for free. You can have this flyer syndicated to many of the top real estate marketing websites....you can also post your flyer to Craig's List (but be prepared to receive lots of spam from this one).
RE/MAX Signature Properties
The National Association of Realtors reports unique visitors to the top 20 Real Estate Websites each month.
The most recent data available is for July. FYI the top 6 are as follows with their number of unique vistors in millions. You can see that the vistors number starts to drop off significantly after the first five. The ranking within the top five tends to shift somewhat from one month to the next, but Realtor.com, Zillow and Trulia tend to be consistently in the top five. Realtor.com usually stays number 1.
Yahoo! Real Estate 7,455
MSN Real Estate 6,400
Good luck, I understand the market is doing ok up there.
Once your listing goes into the MLS it feeds to almost all residential brokerage websites now (if you find a real estate website that doesn't have your listing once posted I wouldn't worry about it. Just means that company hasn't adjusted their web model to meet the online home buyer demands and therefore they are insignificant).
The listings from Realtor.com come from all the local MLS sites. You can have your listing posetd on MLS for a fee, but you can't do enhanced listings.