Some questions for our Bolivia experts

You can definitely arrive in Uyuni at 2am and get on a tour the same day. I've done it twice. Once I just showed up and once I emailed the agency ahead of time.

Potosi is not a comfortable place and depending on when you'll be there it could be really cold. One night can be enough if all you do is the mine and a few sights in town.

Oruro is skippable, especially if you're going to Potosi, although its not without merit of its own.

Tupiza is nice for one or two days if you like walking (in the canyons nearby). There are hotels just as good as elsewhere in Potosi (if I remember well, the Tourist has central heating).

Re your questions about tours from Rurre/Rurrenabaque:

I can refer to these threads:
Bolivia Pampas vs Jungle tour, 03-Sep-2009.
Parque Manu or Parque Manini, 24-Oct-2008.
("Manini" is a misspelling of Madidi).
Mapajo Eco-Jungle Trip - Rurrenbaque, 17-Jan-2010.
I want to visit the Kaa-Iya del Gran Chaco NP and Maididi, 22-Nov-2009
("Maididi" is a misspelling of Madidi).

By using the search function here at the Thorn Tree it is rather easy to find more information.
For instance try a search for: Rurrenabaque jungle pampas
(And another search for: Rurre jungle pampas)
Among the results is this thread: Animal friendly pampas tour?, 25-May-2009

The ecolodges of Mapajo, Chalalán and San Miguel del Bala are in the jungle = in the rain forest.
These and other ecolodges are mentioned at TuSoCo.com = Red Boliviana de Turismo Solidario Comunitario and/or at Turismo-Comunitario.org.

About Mapajo: Strange to say, the web site mapajo.com has disappeared. The registration expired 2010-02-05.
To retrieve the site, try the Internet Archive = WayBack Machine at http://www.archive.org

About the 3 mentioned ecolodges reached from Rurrenabaque: What is the point, the advantage ?
They all offer tours (packages) from Rurrenabaque. I can mention 3 points:
a. Ecological sustainability. But - admitted - adapted to reality and to what is possible. For instance they use boats with motors for the visitors (tourists).
b. Wild animals are not touched or fed. (This is the great problem at most pampas tours).
c. They are community based and community-run.

The importance of 'a' and 'b' depends on your attitude. But 'c' - the community aspect - is always important. You will get a genuine experience, meeting the local people, visiting their village.

The above-mentioned community-run operators have good guides, giving you a unique and authentic experience, and you will support the local inhabitants who want to preserve the nature and maintain their way of living.

Oruro is best seen from a speeding bus or, even better, through the window of a LAN Airbus 320 from 30,000ft. That said, parts of the surrounding area are definitely worth exploring if you've got your own transport, but the city itself is grim in all respects, and all mention of it ought to be purged from the guidebooks.

(Disclaimer: anyone who likes suffering hours of the same interminable dancing and three-legged-donkey-music through wee-stinking streets while dodging staggering locals/the amorous advances of middle-aged Bolivians/water balloons, while getting (i) drunk, and (ii) your pocket picked, should disregard the above advice during Carnaval.)

Tupiza has horses for hire, some nice walking scenery and basic tourist infrastructure - e.g. restaurants, hotels (one with a nice pool) - but other than that is a fairly sleepy place. Attractive setting and a good spot to recharge batteries after a spell on the road/in the campo but not much to do beyond the above and relaxing.

For me, the mines in Potosí are a must. If you're interested in colonial history there's enough else to keep you in Potosí for a few days (e.g. the museum in the old mint, religious stuff to see) but if not a night or two would probably be enough. Out of all the cities/major towns in the altiplano, Potosí has the worst climate, which is fair enough given its altitude, but I actually quite like the place.

Potosí was very enjoyable in February, with warm temperatures, pleasant even at night. Spent three nights there, and 4-5 nights would have been perfect (we still missed a dozen churches, did only the briefest mine tour, did not see the surroundings and dined at none of the recommended restaurants). Lodging, as always, is available for cheap if you look on site. We walked from the plaza into a random side street, and found a double with TV and private hot shower for around 10 US$.