Sounds like it should handle two showers with the newer low flow heads. I wonder about the btu's. Does the natural gas input line need to handle a 165,000 btu gas flow? Thanks in advance.
Found water heater comparison info at http://www.takagi-usa.com/web/tankless.htm
Found a price of $995 at http://www.globaltownewarehouse.com/HomeProducts/cfgorder.htm
Looks like they are 2 to 3 times the price of a regular water heater. The 3.6/3.7 gpm flow would be the minimum for my house with 2 showers going at once or a shower and the washer so I wouldn't want a smaller unit. Hopes this all helps the original poster and she should check the brand and size she is being offered and do a search on the net.