Went Tankless about 1 year ago now and will never go back. Everyone has pretty much expressed the basics already. The real key for me was to figure out the lowest temp of the water ever coming into our house (found on our water companies website) and use that to find the water heaters pressure capability at that temp (found in model information). I think a common problem with tankless units is undersizing them. 

We have a Rinnai RU98i, run on natural gas but can supply enough pressure for 2 showers and a 3rd appliance during the coldest times of the year. 

I ended up installing the autocir pump.  Post 15 above has a picture of it.  Water from showers and faucet are hotter now!  Let me tell you, it was the best thing I could have ever done for my house!   Everytime I turn on the hot water, the water is hot both upstairs and downstairs!  My wife is SO happy now!  I laugh every time I think about it!  Mine is set to keep water hot between 6AM and 1AM.  It's the best investment ever!

I was thinking about getting something like that the autocirc for my house.  I have a tankless water heater and my only complaint is how long it takes for hot water to get to the tap.  If I am just washing my hands, I might as well just use the cold water because it will never be warm before I'm done.

I installed a tankless heater a few years ago and love it! Significant savings on the gas bill. The Bosch model that I have does not allow the use of a recirculating pump though.

Don, the recirc pump sends cold water in the line back to the water heater.  I think it will solve your problem.  I thought about my situation for years before installing the pump.  Back around 10 years ago, there was a guy on the internet called Dan Holligian.  One of his experts showed how to install one of these step by step.  I recorded the video on tape and went on line a printed out the steps but never installed it until this year.  Right now, I'm looking on line to see if Dan Holligan is there and can't find the link.  Anyway, Amazon sells them but maybe cheaper on eBay.  Read the reviews before you buy and take some negative commits with a grain of salt.  Some comments are just not true.  Here's the link for Amazon:  http://www.amazon.com/Laing-LHB08100092-AutoCirc-Recirculation-Timer/dp/B0046MDAK0

However, I did not pay that much for mine.  I think I paid $40 bucks on eBay back in 2007.  Again, mine works perfect!