I typically use a Gateway M-285 Tablet PC. However, this week it's in the shop and I've got a loaner E-155 Tablet PC. Let me start off by saying that this is really an apple and oranges comparison. About the only way's that they are similar is that they are both Tablet PC's from Gateway running Vista. That's about where the similarity ends.
I found the E-155 reasonable for running applications but it was definitely slow compared to the M-285. The difference was very noticeable when running Visual Studio. The E-155 has a 1.2Gig processor with a gig of RAM. The M-285 has a 2.0Gig (as best I can recall) processor with 2 gigs of RAM. Both are Duo processors.
The E-155 has a WACOM screen which is active/passive. What I mean is I can hover the stylus over the screen with out touching and it displays the pointer. However, I can also just use my finger to push buttons as well. The M-285 has an active only screen, which means you have to use the special stylus. I must say, after experiencing the WACOM screen I do prefer the feel of it over the M-285's very slick glossy screen. The WACOM screen seems to have sort of a matte finish which I like. The E-155 screen is 12" which seems a little small, but the display is very crisp. The M-285 14" is an outstanding display, although over time it seems to have gotten a little bit dimmer.
I typically use my tablet along with a docking station and external monitor. Here the E-155 really falls down. The video coming out of the external port is downright blurry. I'm sure this is due to the fact that it's using an integrated video adapter with shared memory. The M-285 I use has been upgraded to a video adapter that has dedicated memory and it was worth it. The M-285 external video is very nice, I typically run an external monitor at 1280x1024 with it.
A nice feature of these tablets is that they share the same docking station. So the video comparison was with the same docking station and monitor. I did also try plugging directly into the E-155's external video adapter and it was still just as bad.
The E-155 has the M-285 beat in the portability department. I also like that the way the fan vent is arranged it is on the "top" side when in my typical tablet orientation. The E-155 case is rubberized in the palm rest area which feels down right weird. The E-155 is much lighter than the M-285. A large part of the weight of my 285 is due to the 12-cell battery that I went with. I typically get 4-5 hours of use out of it. The E-155 gave me several hours of use on it's standard battery. I started off in High Performance mode and dropped to Balanced before needing another battery. Another thing I really liked about the 155 is it's built in fingerprint reader. This made it very nice to be able to quickly unlock the machine. It's something I'll look for on my next tablet.
Sound quality is good from both of the tablet's. Better than many other laptops out there. I haven't had much luck trying to record from the M-285's built in microphone. I have not tried the E-155's dual mic's.
Overall, I very much like both tablet's. The E-155 is a nice device for running Outlook and OneNote and doing general computing tasks. It can be pressed into development service but it won't like it... neither will you! The 155 is so slim and light weight you won't hesitate to grab it before leaving the office. The M-285's weight help's keep up your arm strength. But it won't balk at doing whatever you ask of it. It is not unusual for me to have the 285 running Visual Studio, NUnit, SQL Server, IIS, Outlook and OneNote simultaneously. If I could keep both machines, I could see some benefit in that. I'd get rid of the PDA and use the 155 primarily for Outlook, OneNote, running a few client side tools and as an eReader. If I could have only one machine, it would likely be the 285 with dock. Gateway has the 295 out now. The 295 it seems to me is a slightly upgraded 285 with the WACOM screen.