I also have a pair of ML Summits - mine are around 17 years old now. I purchased them second hand this year - the previous owner apparently had then "serviced" by Absolute Sounds but I don't think anything was really done.
ML say that the panels are tough - they would even survive being perforated and still perform satisfactorily, although I think you'd have to be going some (or sat in front of them with a pin) to get through the metal stators either side of the membrane! A quick vacuum every couple of weeks to keep them dust free is all the maintenance they really need, plus a damp cloth over the bass enclosures.
As has been mentioned already there's two basic types of ML electrostatics - full range ones such as the CLS / CLS II / CLX or the much more common hybrids that combine an ESL panel to handle frequencies from around 300Hz (model-dependent) upwards, allied to a conventional cone-driver to handle the bass. The hybrid models also come in two main categories, those that are purely passive and those that have built-in amplification for the bass section (the ESL panel itself is always passive). The former type includes models such as the Aerius, Clarity, Sequel and the current Electromotion. The latter type include the Summit , Summit X, Montis and all but the smallest model in the current Masterpiece range (the Classic) which is still a passive model. All models only have speaker-level inputs - if it's a semi-active model then the internals sort out splitting the signal between panel and bass section and deal with A-D conversion where necessary.
Older hybrid models suffered (apparently) with poor integration between the bass and panels, I never heard any so can't comment. Since the Summit / Montis were introduced that seems to have changed significantly, personally I'm not aware of any major issues in this area, the transition from the lower frequencies to the panel seem pretty seamless to me, both in tone and pace. The full range models are probably a bit of an acquired taste - brilliant at what they do within the limitations (i.e. no deep bass) but I auditioned a pair of the original CLS some years ago and couldn't have lived with them. The Statement might be a different matter, but you'll need to be living in a stately home to fit them in!
They do like a bit of space around them - given the dipole nature of the panels you need to give them a good amount of distance to the front wall, and potentially consider room treatment to manage any excessive rearward radiation. ML recommend 2ft upwards I think, the further away the better really. They can work well surprisingly close to side walls though - that's the main reason I wanted to try some because I have a narrow room so any speaker ends up positioned quite close. Obviously there's still interaction but it's reduced compared to the dispersion pattern of a conventional driver. Recommendation is to have one of either the front or rear walls with "hard" surfaces and the other one "soft", I can't remember where I read that but it seems to work for me.
Also be aware that many models are a bit of a bugger to drive properly. Although the "nominal" impedance is often quoted around 4 ohm, it varies significantly. They have reactive impedance curves and dip very low at the top end of the frequency range - sub-1 ohm in the case of our Summits so they like an amp that can really drive them and cope with that sort of environment. I know that reviewers have often said they've tried them with valve amps but really I wouldn't say that's a great match unless you have a really "grunty" one with a high damping factor, or you'll lose the top end. Lots of high quality solid state amps are where it's at! John uses Nord Class-D monos with his and I have a Class-D Audio Research integrated and both are very successful. Perhaps contrary to logic, the amp you choose to partner does
have an impact on the bass of the semi-active models, even though they have their own amplification.
The current range of semi-active hybrids have a more sophisticated bass management system than our somewhat basic 25 / 50 Hz level controls. You can plug in a microphone and use the Anthem Room Correction system (basically a DSP engine) to even out bass response in-room. Some people like it, some don't but it's an option.
Small changes in positioning can make a significant difference in certain rooms. Playing around with this can make or break your relationship with MLs. Get it right and you won't want to go back to conventional speakers. They can do imaging (focus, separation, scale, clarity) like no other and really communicate the soul of the music. I'm still playing with my setup but it's fun to hear the changes as you play around.
P.S. The Martin Logan website is a good resource for finding out about older models - they have a product museum
(<- link) that includes a timeline and literature about most of the older models