nl_carey

The only two really at all different areas are having to carry bailout, and having the double-hose.
Bailout will be simple, just add an extra clip on your line, and bob's your uncle. I find it easier to put bailout on in-water, but normally do it before jumping in just so you don't forget anything!
The hose is a problem sometimes depending on the rebreather and how easy it is to get at if it's sitting behind your head. In-water though, this isn't significant, you can just duck under it or set it up to be out of the way whilst you stuff yourself in.
Two other issues that could be a problem if you dive on your own:
1. Bubble Check - most Rebreather divers prefer to have a bubble check at ~5m or so before continuing, as small problems can cause minor bubble loss. If you're noticing bubbles, it can be very difficult to determine where these are coming from in-water.
2. Weight. Some Rebreather's are very heavy when fully equipped with weights etc. Not heavy compared to big sets of twins, but heavy compared to singles, for example. Pulling these up the side of the boat can be a handful on your own, particularly if you're buggered after a dive. Some units like the PRISM, Sport KISS, Mini-Meg and Evolution are lighter than others though. Some modified O2 rebreathers are really, really light!