Same here - made plenty of 30 minute connections at VIE, FRA and MUC. Never missed one.

OS are decent enough - if you're on an MD80 or a F70, it's not great. If you're on an A320 or A321, the planes are lovely, and the seats among my favourite short-haul Y. If it's a Lauda 737 or 767, the planes are a bit old, and the seats a bit hard, but the catering is out of this world.

VIE is a compact airport, but ease of connection depends on luck. The A-gates are non-Schengen, and the C-gates Schengen. You're non-Schengen to non-Schengen, but... Some of the C-gates are dual purpose, and can be set up with a passport control desk if used for non-Schengen. In the case of an A-C or C-A non-Schengen transfer, you'll have to wait for a bus (unless, of course, you have a Schengen visa, and are willing to go through two sets of passport control). C-C transfers are easy - you can walk to the gate directly. Security is at the gate.

FRA will be a trickier one for you. Your LHR-FRA flight will most likely land on the upper floor of the A pier, and your FRA-MOW (is it SVO or DME?) from the B pier. This means a ride on the SkyLine, and a 10 minute walk at the B station. It's still doable (I've made a 15-minute connection before), but you'll be rushed. If you decide to do LCY-FRA, however, you'll be bussed to B, making it easier.

WAW is a very compact little airport, and transfers are easy. No problems there.