I am currently using a laptop. An IBM t20 750 Piii with 256 meg ram.
I am getting great results with it. Currently I am using the stock soundcard, as I keep waking for more firewire/pcmcia/usb2 alternatives. Also, it is a company computer and its lease is up in August so I am going to wait until then to see what I get to replace it.
I am running Sonar 2, use
an evolution mk249c for soft synths and control sufracing. Very littel latency, barely ever crashes or has dropouts. I have run as many as 25-40 tracks at once, with a few plugins. with no problems. As far as # of recorded tracks at the same time, I only can do 1 at a time given the current soundcard situation.
I had ordered the Hammerfall HDSP but the release date kept getting pushed back, and I understand they are still hard to get in the states. In EU I hear it is easier. The only reason I would not get it now is that they don't support WDM drivers, which Sonar needs. RME says they can still get 3ms latency, but I am worried without WDM. If that wasn't an issue I would probably get that one.
The echo products seem like the choice I will go with, unless Presonus' firestation really knocks my socks off. Motu stuff isn't interesting to me b/c of their mac heritage and I haven't heard the greatest things about their support. Lastly, Metric Halo's mobile i/o looks like the best option, but they don't support PC drivers yet. They say they will soon, but when I inquired they said, "I don't know, maybe a few months". Not too encouraging.
I cannot go back to PC recording after using the laptop. I sue it everywhere. Mixing on trains, recording in hotel rooms. Even at home, I find myself easily being able to record in different rooms, etc.
Hard drive speed is an issue. Laptop specs often don't even mention it. Some I have seen are now 5400 and some sony's have 7200 drives. Firewire drives are another option.