Well reading reviews on it I'd say that flash drives are much much faster at loading stuff so the boot up time must be quick. Two problems with that atm though, they are small in size and they are bloody expensive.

SSD is solid state drives.... right? I don't have any experience with them so I'm no more help than google at this point, sorry.

sup i been following this stuff pretty extensively since they're all cool/cheap.  i have a first gen eee that i bought when they first came out, so i don't have as much first-hand experience with atom and how they do with xp as i do with their little linux distro, but i would say whether or not you want an ssd depends on what you're going to use it for.  if it is purely for work and you do not need to store anything but EXCEL DOCUMENTS then get one, because they're ultra fast and boot in like 12 seconds, and the battery is pretty alright, too.  but!!  if you want like... an actual notebook that you would also be using for other stuff then i would advise against getting one because a) their capacity is terrible for the most part, and b) they're much more expensive than traditional hdds, especially the 48gb ones.  the speed improvement, aside from boot speed, isn't THAT big a deal.  also a lot of the netbooks that come equipped with ssds don't actually have especially good battery life (3-4 1/2 hour range), and some of the ones that come with traditional hdds instead end up topping that.

eees are basically trash now, though.  asus had a good lead, but ruined it by putting out about fourteen thousand fucking models and losing sight of the fact that they're supposed to be budget notebooks.  atm hp makes one but it's also too expensive, so if you're seriously looking into one, i'd suggest the msi wind.  it's gotten really good reviews, and is looking to be the successor to the first wave eees.  i've used one for a bit and my impression is that 1) the boot speed is okay, but not as impressive as an ssd.  w/e though, the actual speed it runs files off the hdd with is fine, 2) it runs vista alright but xp quite a bit better, so i would suggest that, but with xp the atom cpu is pretty great!  it's very speedy, and to answer your question the little bit i've fooled around with ms office/photoshop/other shit, even with an hdd, i was impressed with how fast they loaded up and were (i've heard vista is substantially slower than xp with this though!), and 3) despite not having an ssd, the battery life is better than on my eee, and a lot of other ssd-based netbooks.  i think it gets around 5-7 hours or something ridiculous like that.  it might be available with an ssd, which would basically make it baller since it's already got a good processor and excellent battery life.

also another reason not to get an eee is because, even though you can adjust, the keyboards pretty much blow.  even on the bigger ones, the keyboard hasn't gotten any larger or more comfortable.  the hp mininote made improvements in this respect, but msi really nailed it.  for a 10" computer, it's about as comfortable to type on as any full-size notebook keyboard i've used.  the wind's between $400-500, i believe.  they might be difficult to find, though, because i think they're pretty popular.  i think the mininote has that shitty glossy screen, too, which the wind doesn't.  also the eees look like toys, and the mininote/wind look like actual notebooks, so that's a plus.

The thing about them having shorter battery life is that I don't think SSDs are inferior to HDDs in terms of power consumption, I just think the ones I've used have had shitty batteries.  I'm sure if you used the same netbook/battery with both types of drives, the SSD would come out ahead, but a lot of those cheaper netbooks, perhaps in part because of how expensive SSDs are, skimp on the batteries and other stuff.  The more expensive ones around $500 have in my experience been better in regards to this, even with HDDs, so I'm sure if you're a nut for battery life, it'd only get better if you opted for an SSD instead in one of those.

Also, I forgot about the S10.  The keyboard looks like it might be a little cramped, but none of the shots I've seen have really shown it all that well, and honestly it is cheaper/more feature-packed than the Wind, so I dunno!  It's really cool that it has a bigger hard drive, and comes with bluetooth/an express card slot, and they look really nice too.  Plus, Lenovo is a really good company I think, and I wouldn't blame you for being hesitant about MSI's notebooks.  I'm not sure you can get that specific version outside of China, though, and their 9" one probably won't be as nice.